CA3224968A1

CA3224968A1 - Functional reactive layer helmet

Info

Publication number: CA3224968A1
Application number: CA3224968A
Authority: CA
Inventors: Robin Spicer; Adam LEVY; Henry NEILSON; James Cook
Original assignee: Hexr Ltd
Current assignee: Hexr Ltd
Priority date: 2021-07-13
Filing date: 2022-07-13
Publication date: 2023-01-19
Also published as: AU2022311511A1; JP2024524659A; WO2023285576A1; US20240315373A1; EP4369974A1

Abstract

The present invention relates to a helmet (1) comprising: a first layer (10) forming an outer surface of the helmet (1), a second layer (30), and a reactive layer (20) sandwiched between the first layer (10) and the second layer (30), whereby said reactive layer (20) comprises a plurality of rigid balls (2) allowing the first layer (10) to roll upon the second layer (30) as soon as the helmet (1) undergoes an impact of an intensity greater than a predetermined threshold.

Description

Functional Reactive Layer Helmet Specification The invention relates to an impact mitigation structure, particularly a helmet, particularly a helmet for cycling, as well as to a method for producing such an impact mitigation structure, particularly helmet.
Injury to a person or damage to an object can occur when the person or object is subjected to an impact of sufficient magnitude. Considerable developmental effort has been expended to produce helmets which provide protection from potentially damaging or injurious impacts.
Head injuries, which can be incurred as a result of participation in sports such as cycling are a common cause of serious brain injuries.
A brain trauma may occur as a consequence of either a focal impact upon the head, a sudden acceleration or deceleration within the cranium, or a combination of both impact and movement. Impact protection is therefore important in preventing brain injuries as a result of impacts to the head.
Head protection, in the form of helmets, is designed to reduce the forces experienced by a user's head during an impact. Generally, a helmet comprises at least one impact absorbing layer which is designed to absorb a portion of the forces to which the helmet is subjected during an impact.
However, helmets often do not provide adequate protection during an impact against both linear and tangential forces. As oblique impacts are common, impacts will often include both linear and tangential components. Particularly, an oblique impact means that the force acting on the outer surface of the helmet that is e.g. hitting the tarmac upon a crash comprises a component that extends tangentially with respect to said outer surface at the location of the impact.
Unfortunately, such tangential forces in particular result in the rotational acceleration of the brain, which has been linked to bridging vein rupture. In turn, this may be responsible for subdural hematomas, and diffuse axonal injuries. Tangential forces during an impact may also result in neck injuries.

2 Based on the above, the problem to be solved by the present invention is to provide an improved helmet that is capable of reducing the above-mentioned injuries related to oblique impacts comprising a tangential force acting on the helmet / head of the person wearing the helmet.
This problem is solved by an impact mitigation structure, particularly helmet, having the features of claim 1 and a method having the features of claim 51.
Preferred embodiments of this first aspect of the present invention are stated in the corresponding dependent claims and are described below. Furthermore, further aspects of the present invention are introduced below.
According to claim 1, a helmet is disclosed, particularly a cycling helmet, comprising:
- A first layer forming an outer surface of the helmet, - a second layer, and - a reactive layer sandwiched between the first layer and the second layer, and preferably connected to the first and second layers.
In the following, the invention is described predominantly with respect to a helmet. However, according to a second aspect of the present invention, an impact mitigation structure is disclosed. Since the underlying principle of the present invention does not only apply to helmets, but impact mitigation structures in general, the notion of a helmet can be replaced in all embodiments and aspects of the present invention by the more general notion of an impact mitigation structure. For example, apart from a helmet, such an impact mitigation structure can be car bumper, a crash barrier, a paintwork (e.g. in key locations on a vehicle), a body part of a vehicle (e.g. car body), protective armor.
In the following features of the first layer are described as well as its interaction with the reactive layer and the second layer. It should be noted however, that the helmet preferably comprises several such first layer that can be arranged side-by-side on the second layer of the helmet, with a corresponding number of reactive layers arranged between the respective first layer and underlying second layer. Thus, all features and embodiments described below with reference to one first layer also apply to embodiments where the helmet comprises a plurality of first layers and reactive layers (which can form membranes, see below). Furthermore, in all embodiments, the second layer can be formed in one piece, but can also be formed by multiple sheets arranged side by side (particularly on the energy absorbing layer, see below).

3 Furthermore, according to an embodiment, adjacent first layers/panels can be shaped to have a ramp that facilitate direction and free movement of a first layer (over the respective ramp).
According to a preferred embodiment, the first and the second layer are stiff layers, wherein said stiffness is particularly due to material (modulus of elasticity) and shape of said layers. A
material that is stiff can withstand high loads without elastic deformation.
Typically, thin sheets of polycarbonate can be used as basis of said layers which result in sufficiently stiff structures when being arranged in a curved configuration adapted to the shape of a head of a person.
According to a preferred embodiment of the helmet, the reactive layer comprises a plurality of rigid balls (e.g. spherical bodies), that particularly remain rigid during normal use of the helmet and are configured to roll at an impact threshold over an outer surface of the second layer (so-called B surface). This means that in case a pre-defined tangential force acts on the first layer due to an oblique impact (e.g. helmet and head therein hitting the ground) exceeds a predefined threshold force, said rolling is initiated.
In this context "rolling over" an outer surface of the second layer does not necessarily mean that there is a contact between the balls and the outer surface of the second layer, since intermediary layers can be arranged between the balls and said outer surface of the second layer. Therefore "rolling over" also includes rolling on such an intermediary layer. Particularly, as will be described further below, the balls form part of the reactive layer that can be a membrane comprising a substrate film to which the balls can be bonded by means of an adhesive, wherein the substrate film can be bonded by an adhesive layer to the outer surface of the second layer. Thus, here, the balls may roll on the substrate film and said adhesive.
Furthermore, the balls do not need to be spheres and may deviate from a perfect spherical shape. Therefore, the notion of a ball according to the present invention therefore includes rollable elements and the balls may also be referred to as rollable elements.
Furthermore, the first and/or the second layer do not need to be homogenous layers, but can each consist of different materials and/or layers stacked on top of one another.
In a preferred embodiment, the balls can be formed out of polycarbonate.
According to alternative embodiments, the balls can be formed out of one of the following materials:
polystyrene (PS), acrylonitrile butadiene styrene (ABS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), poly(methyl nnethacrylate) (PMMA). Each of these materials can be used in conjunction with all other embodiments of the helmet described herein.

4 Preferably, according to an embodiment, the rigid balls are formed from a material comprising a Young's modulus (modulus of elasticity) in the range from 0.5 to 10 GPa.
Particularly, according to a preferred embodiment, the balls comprise a diameter in the range from 0.5 to 5 mm, wherein particularly the diameter is 2 mm.
According to a preferred embodiment of the helmet, the balls are distributed along an inner surface of the first layer such that they cover an area that corresponds to 10% to 50%, preferably 15% to 30%, preferably about 20% of the area of said inner surface.
Particularly, the lower this packing density of the balls, the better for product weight.
Particularly 20% density (of surface area covered in balls) is close to the lower limit where any lower density may allow the inner surface of the first layer to be depressed by hand between adjacent balls. Thus, there is an inverse correlation between ball packing density and stiffness of the inner surface of the first layer and outer surface of the second layer.
Furthermore, according to a preferred embodiment of the helmet the balls of the reactive layer are bonded to a substrate film via an adhesive configured to undergo brittle failure. The substrate film can be formed out of a polymer, particularly PVC. According to preferred embodiments the adhesive is one of the following adhesives: Cyanoacrylate, polyvinyl acetate (PVA), epoxy.
According to an embodiment, the rigid balls in the reactive layer are bonded to a substrate film via a primarily brittle-failure-based adhesive.
Furthermore, according to a preferred embodiment of the helmet, the substrate film comprises a thickness smaller than 200 pm.
Further, according to a preferred embodiment of the helmet, the substrate film comprises an adhesive layer preferably consisting of a pressure sensitive adhesive arranged on a side of the substrate film facing away from said plurality of balls.
Furthermore, according to a preferred embodiment of the helmet, the reactive layer is or comprises a membrane bonded to the first and the second layer, wherein the membrane comprises said substrate film and the plurality of balls arranged thereon.
Particularly, the membrane can comprise a vinyl both for wet and dry applications.
Further, preferred, the membrane or the substrate film is bonded to the outer surface of the second layer via said adhesive layer consisting of said pressure sensitive adhesive of the substrate film.

5 Furthermore, in an embodiment, the membrane or the plurality of balls is bonded to an inner surface of the first layer (so-called A surface) via an adhesive layer, preferably an adhesive layer comprising (or consisting of) a thermo-softening adhesive. Particularly, the adhesive becomes active during high temperature moulding and therefore allows to bond the balls of the reactive layer to the inner surface of the first layer in a mold in which a portion of the helmet is formed.
Furthermore, an embodiment, the first layer comprises: a sheet (the sheet being preferably formed from a plastic material such as polycarbonate (PC)), a color layer (e.g. a colored ink layer) arranged on an inner surface of the sheet, a protective layer arranged on the color layer, wherein said adhesive layer that bonds the membrane to the inner surface of the first layer is bonded to the protective layer. A further coat such as a light bleed preventing coat (see also below) can be applied to the color layer before the protective layer is arranged on the color layer / further coat.
However, according to a further preferred embodiment of the present invention, instead of using a membrane, the balls can be bonded (e.g. directly) to the outer surface of the second layer with an adhesive, particularly an adhesive comprising PVA (poly(vinyl alcohol)).
Particularly, in all embodiments, the outer surface of the second layer faces outwards, i.e., away from a head of a person wearing the helmet, wherein the inner surface of the first layer(s) faces towards the head of said person wearing the helmet.
In preferred embodiment of the helmet, the protective layer is a heat resistant ink layer.
Particularly, the heat resistant ink layer can be screen printed or UV printed onto the color layer (e.g. colored ink layer) or the coated color layer (see above).
According to a further embodiment of the helmet, the protective layer is a polymer layer, particularly a polyvinylchloride layer. Other materials such as PC can also be used instead of PVC.
Furthermore, preferably, the respective protective layer comprises a thickness below 0.1 mm and/or a yield strength larger than 20 MPa according to an embodiment of the helmet.
Further, according to a preferred embodiment of the helmet, the protective layer has a thermal expansion differing less than 5 ck from a thermal expansion of a material of the first layer.
According to yet another embodiment of the helmet, the first layer is a twin sheet assembly comprising an outer sheet and an inner sheet being thermoformed simultaneously in particular, wherein both sheets preferably consist of polycarbonate (PC).

6 Preferably, in an embodiment, the inner sheet of the twin sheet assembly is perforated, particularly so as to allow the negative pressure of the forming to pass through to the outer sheet so that not only the inner sheet is pulled down onto the forming.
Furthermore, in an embodiment, a color layer (particularly a colored ink layer) and an adhesive layer (particularly an adhesive ink layer) are arranged between the outer and the inner sheet, wherein particularly the color layer is arranged on the outer sheet and the inner sheet is bonded to the outer layer via the adhesive ink layer and the color layer.
Further, according to a preferred embodiment of the helmet according to the present invention, the helmet comprises an energy absorbing layer, wherein an inner surface of the second layer bonded to the energy absorbing layer by an adhesive layer (e.g., acrilux).
Such an adhesive can comprise 25% to 30% titanium dioxide in powder form containing 1% or more of particles with aerodynamic diameter below 10 pm (CAS 13463-67-7). Further, the adhesive (e.g.
acrilux) can comprise 25% to 30% 4-hydroxy-4-methylpentan-2-one; diacetone alcohol (CAS
123-42-2). Further, the adhesive (e.g. acrilux) can contain 15% to 20% 1-methoxy-2-propanol;
monopropylene glycol methyl ether (CAS 107-98-2).
Furthermore, according to a preferred embodiment of the helmet, the second layer comprises recesses (e.g. at an edge of the second layer) and/or through-holes through which portions (e.g. through-welds) of the energy absorbing layer extends towards the first layer, said portions of the energy absorbing layer being bonded to the first layer (through-weld).
Particularly, the first layer comprises said adhesive layer (e.g. thermo-softening adhesive) arranged thereon, wherein said portions of the energy absorbing layer can be bond to the first layer via said adhesive layer. Alternatively, said adhesively layer can be completely or partially omitted and said portions of the energy absorbing layer can be bonded to the first layer (i.e. without said adhesive layer as an intermediary layer).
Preferably, according to a preferred embodiment, the outer surface of the second layer locally bends upwards around the respective recess and/or through-hole to reduce a separation between the inner surface of the first layer and said outer surface of the second layer, particularly so as to avoid a bleeding of the energy absorbing layer into a volume between said inner and outer surfaces during manufacturing of the energy absorbing layer.
According to a preferred embodiment, the energy absorbing layer comprises polystyrene, preferably expanded polystyrene (EPS) or polyurethane, particularly expanded polyurethane (EPU), or polypropylene, particularly expanded polypropylene (EPP). For a molding process, where the energy absorbing layer is formed adjacent the first and the second layer and the intermediary reactive layer (e.g. membrane) using preferably an in-moulding (see also below),

7 the material for the energy absorbing layer can be provide in the cavity of the mould as bulk material (e.g. in the form of pellets).
Further, according to a preferred embodiment of the helmet, the reactive layer is configured to facilitate relative movement between the first layer and the second layer by the rolling of balls of said plurality of balls between the first and the second layer (i.e.
between the A surface and the B surface), wherein said rolling of balls provides a low rolling resistance in the range from 0.0001 to 0.2, preferably in the range from 0.02 to 0.05, preferably in the range between 0.025 to 0.04 between the balls and an inner surface of the first layer or an inner surface connected to the first layer or between the balls and an outer surface of the second layer or an outer surface connected to the second layer, wherein particularly said range applies to the interface with the lower rolling resistance. A particularly preferred rolling resistance amounts to about 0.025. Another particularly preferred rolling resistance amounts to about 0.04.
It is to be noted that the rolling resistance relates to the surface that the balls actually contact.
Therefore, in case intermediary layers are present between the first layer and the balls, the latter roll on a surface connected to the first layer (i.e. a surface formed by the respective intermediate layer). Likewise, in case intermediary layers are present between the second layer and the balls, the latter roll on a surface connected to the second layer (i.e. a surface formed by the respective intermediate layer).
Preferably, the rolling of the balls between the A and B surfaces provides an extremely low resistance-to-motion (RTM) (in this context rolling resistance, could also be friction or any other mechanical/geometric resistance) form of movement. However, employing rolling does not intrinsically make the movement occur more readily, it merely lowers the lower limit, allowing other movement inhibiting mechanisms to become the dominant factors (i.e.
adhesives and/or connectors initially connecting the first and second layers).
Particularly, relative movement is facilitated between the impacted surface, e.g. the first layer hitting tarmac) and the second layer being fixed with respect to head of a person wearing the helmet thus reducing risk of traumatic brain injury (TBI).
Preferably, a separation between the inner surface of the first layer (A
surface) and the outer surface of the second layer (B surface) remains as constant as possible.
Should an impact occur where the balls are required to roll into an area where the separation between the said inner surface and said outer surface is smaller - then they would wedge and the RTM would shoot up. Particularly, according to an embodiment, upon a typical impact said separation varies less then 20%, particularly less than 15%, particularly less than 10%, preferably less than 5%.

8 According to a preferred embodiment of the present invention, the balls of the reactive layer are bodies (particularly round or ellipsoidal bodies) comprising a roundness above 0.7, more preferably a roundness above 0.8, more preferably a roundness above 0.9, more preferably a roundness above 0.95, more preferably a roundness above 0.97, more preferably a roundness above 0.99. Preferably, in an embodiment, the balls are spherical bodies.
With respect to a cross-section of a ball that extends orthogonally to an axis of rotation of the ball about which the ball can rotate, roundness is defined as the ratio between the area of a circle inscribed in the cross-section and the area of a circle circumscribing the cross-section, i.e., the maximum and minimum sizes for circles just sufficient to fit within and enclose the cross-section.
According to an embodiment, the balls preferably comprise a constant diameter and/or volume.
According to an alternative embodiment, the balls comprise different diameters and/or volumes.
According to yet another embodiment, the balls can be solid bodies or hollow bodies.
Further, as the second layer moves relative to the first layer, particularly under the first layer, the outer surface of the second layer and the inner surface of the first layer preferably maintain their congruent relationship. Therefore, according to a preferred embodiment, the inner surface of the first layer (A surface) and the outer surface of the second layer (B
surface) are concentric with respect to one another.
During an impact there may be enough energy to flatten the A and/or B surfaces enough to affect the predetermined congruency and concentricity factors. Stiffening the B surface (in particular) reduces the deformation magnitude. Furthermore, as the B surface moves under the A surface, the B surface can become exposed as balls roll away. If this exposed portion can make contact with the impacting surface, then a shear force can be transferred, increasing the RTM drastically. This issue can be mitigated by ensuring that all impactable locations are protected by the reactive layer. According to a preferred embodiment, the first layer(s) and the reactive layer(s) therefore cover at least 50% of the outer surface of the second layer, preferably at least 70%, more preferably at least 80%, more preferably at least 90%.
According to yet another preferred embodiment of the helmet according to the present invention, the membrane or reactive layer is congruent to the inner surface of the first layer.
Particularly, if the force of an impact is not spread over a large enough area then local loading of the reactive layer can be too large which may lead to a flattening of balls and/or ball indentation an adjacent surface such as the inner surface of the first layer and/or the outer

9 surface of the second layer. This could lead to an increased RTM. To prevent either from happening, the camber and undulation of the inner surface of the first layer and an underlying portion of the outer surface of the second layer is preferably as low as possible so that less point loading can occur. Preferably, at any point, a radius of curvature of said inner surface and/or of said portion of the outer surface is larger than 40mm, preferably larger than 60mm, preferably larger than 80mm, preferably larger than 100 mm.
Particularly, as the outer surface of the second layer moves under the inner surface of the first layer, the inner surface of the first layer may start butting up against non-congruent portions of the outer surface of the second layer. In case the outer surface of the second layer is not ramped at these locations to encourage the inner surface of the first layer to bend away, then the inner surface of the first layer may lock up and the RTM will rise.
Furthermore, according to a preferred embodiment of the helmet, the second layer forms at least one ramp to cause the first layer to bend away from the second layer to avoid butting up of the first layer on a portion of the second portion. This is also denoted as edge ramping.
Similar to edge ramping, but in the trailing direction, the inner surface of the first layer may hook onto details of the outer surface of the second layer causing the RTM to rise. This is also denoted as edge hooking. Accordingly, in an embodiment, this is prevented by ensuring the of the of helmet geometry has no hard or sharp trailing edges.
Particularly, according to an embodiment, the energy absorbing layer and/or the second layer comprises an edge portion having a chamfered or rounded edge to prevent a trailing edge of the first layer from becoming caught on said edge portion when moving relative to the second layer and/or energy absorbing layer over said edge portion.
Particularly, according to an embodiment, the reactive layer is configured to hold the first layer such that a tangential force required to activate rolling of balls of the reactive layer is about 0.1kN, or or such that an energy introduced by the impact force (FT) has to exceed a threshold of 2.5 Joule to activate rolling of the balls.
Furthermore, in a typical scenario, the goal of reducing shear forces acting on the brain can be directly correlated to decreasing the RTM of the reactive layer. However, once the RTM
gets low enough, an inverse correlation starts to emerge, where, as the RTM is lowered, the shear forces acting on the brain rise. This is because during an oblique impact two moments act on the helmet, a positive one created between the inertia of the head twisting against the stationary ground, and a negative one created by the center of gravity of the twisting against the normal force of the ground. This means that the lowest resultant moment on the head (which causes the lowest shear forces) happens when the positive moment equals the

10 negative moment. If the RTM gets low enough then the positive moment tends to zero and the negative moment becomes the major moment on the head. This leads to the requirement of controlling the RTM not just diminishing it as much as possible.
One such preferred example/embodiment is to add speed bumps to the outer surface of the second layer that inhibit rolling slightly. These speed bumps can have variable height and frequency to tune the RTM. Speed bumps can overlap in different orientations to affect different impact orientations differently. Thus, according to a further preferred embodiment of the helmet, the outer surface of the second layer comprises a plurality of protrusions (particularly integral with the second layer) forming a corrugated structure, i.e., speed bumps, that inhibit the rolling of balls of said plurality of balls.
Particularly, for certain impact directions the first layer may move towards the face of a person wearing the helmet. To address both perceived and actual danger, this may pose with facial/ocular lacerations, small particle hitting the eyes etc. Therefore, the helmet preferably comprises a corresponding peeling mechanism. This mechanism sees the front-most part of the first layer being bonded to the second layer causing a leading edge of the first layer to remain in place during an oblique impact, and the rest of the first layer to fold over itself.
Preferably, this folding means the first layer's leading edge is curved - not sharp. The curving profile can also retain ejected balls and act like a shield.
Particularly, according to preferred embodiment of the helmet, the first layer comprises a front portion connected to the energy absorbing layer causing the front portion of the first layer to remain in place during an oblique impact in a first direction from a rear of the helmet towards the front of the helmet, while a remaining portion of the first layer being connected to the front portion is separated from the second layer (and particularly folds over itself), and wherein, during an oblique impact in a second direction from the front of the helmet towards the rear from the helmet, the front portion is configured to disengage from the energy absorbing layer or the remaining portion of the first layer is configured to tear apart from the front portion of the first layer.
Further, according to a preferred embodiment of the helmet, said front portion forms a tab comprising an opening, the tab being embedded in the energy absorbing layer (particularly in a front portion of the helmet/energy absorbing layer), wherein a portion of the energy absorbing layer extends through said opening such that said portion holds the tab in place upon said oblique impact in the first direction and breaks to release the tab upon said oblique impact in the second direction.

11 Particularly, to achieve this the front part/ tab can have a thinner cross section as the remaining portion of the first layer and/or the first layer can comprise a predetermined breaking point.
Another way to reduce perceived and actual danger associated with balls ejecting during an impact is to increase the ball adhesion as much as possible while ensuring there is no gain in the RIM.
According to a preferred embodiment of the helmet according to the present invention a first strength of the bonds between the balls and an inner surface of the first layer or an inner surface connected to the first layer differs from a second strength of the bonds between the balls and an outer surface of the second layer or an outer surface connected to the second layer. According to a preferred embodiment, the second strength is larger, particularly so as to retain more balls to the second layer. Preferably, the second strength is at least twice as large as the first strength, particularly at least three times as large, particularly at least 8 to 20 times as large.
Furthermore, edge finishes of the first layer and helmet in general are preferably designed to avoid snagging during everyday use. The length, angle and thickness of the overhang can cause more geometric locking.
Further, according to a preferred embodiment of the helmet, upon an impact force on the first layer, the first layer is configured to deform in shape and move relative to the second layer.
Further, according to a preferred embodiment of the helmet, the first layer comprises an edge region, where particularly the first layer meets the second layer or is coupled to the second layer, wherein the edge region is configured to reduce a transfer of a radial force acting on the first layer from the first layer to the second layer.
Further, according to a preferred embodiment of the helmet, said edge region is formed by a portion of the first layer extending at an angle (x) with respect to a normal of an outer surface of the second layer, said angle (x) being in the range from 20 to 80 , preferably 30 to 70 , preferably 40 to 60 , preferably 40 to 50 . Particularly, the cosine of said angle x (cos(x)) determines the magnitude of transmissible load (for given material properties). If this angle is too small, a significant portion of the impact force is transmitted directly to the outer surface of the second stiff layer instead of the reactive layer, particularly membrane, creating high friction.
If the angle is too big, the majority of the force is transmitted to the intermediary layer allowing it to move relative to the outer surface Further, according to a preferred embodiment of the helmet, the first layer comprises an edge region that is connected to the outer surface of the second stiff layer by a compressible

12 intermediary layer, particularly to reduce a transfer of a radial force acting on the first layer from the first layer to the second layer. For instance, the intermediary layer can be a foam tape or other media that yields readily.
Further, according to a preferred embodiment of the helmet, the first layer is configured to store and release energy as a result of an impact to the first layer to reduce rotational motion of a head of a person wearing the helmet Further, according to a preferred embodiment of the helmet, the first layer is configured to change its shape relative to the second layer during impact, wherein particularly the first layer comprises an auxetic structure.
Further, according to a preferred embodiment of the helmet, the first layer is shaped to pivot the helmet during impact and thereby reduce rotational motion of a head of a person wearing the helmet.
Further, according to yet another preferred embodiment of the helmet, the first layer is configured to deform during an impact such that a free movement of the first layer is inhibited during impact, wherein particularly said deformation causes a peeling of the adhesive bonding the balls to the outer surface of the second layer, particularly via said substrate film and its adhesive layer.
Furthermore, according to a preferred embodiment of the helmet, the first layer comprises a buckling for supporting said pivoting. Particularly, the buckling can have a round shape or a wedge shape. Particularly, said buckling can be configured to snap-through under an impact, particularly oblique impact.
Further, according to a preferred embodiment of the helmet, upon an impact, the buckling is configured to flatten and increase in width resulting in a translational movement of a boundary region of the buckling causing the balls to roll.
This can be used to increase duration at which the reactive layer can operate.
Particularly, as the first layer deforms it can also move relative the second layer. This increases the time at which the reactive layer is working, which may require less reactive layer -less weight, or better controlling dynamics.
Furthermore, advantageously, as the shell deforms, the width increases which helps to reduce the exposure between the first and the second layers. Preferably, the inner surface of the first layer should be hemispherical for better rolling performance. An outer surface of the first layer, via which surface the helmet is impacted in a crash, might not want to be hemispherical for

13 aesthetic or aerodynamic reasons, but may comprise other functional features such as the buckling(s) described above.
Further, according to a preferred embodiment of the helmet, the buckling is configured to provide a redirection of a normal force of an impact acting on the first layer such that the normal force comprises a distance to the center of mass of the system comprised of the helmet and a head of a person wearing the helmet Furthermore, according to a preferred embodiment of the helmet, the first layer, particularly the buckling, is configured to deform on impact to prevent geometric locking of the first stiff layer due to a mechanical interaction with an adjacent structure of the helmet, wherein particularly deformation of the first stiff layer, particularly of the buckling, causes an edge region of the first stiff layer to lift up from the reactive layer so as to not become entangled with adjacent structures of the helmet.
Furthermore, according to a preferred embodiment of the helmet, the inner surface of the first stiff layer is configured to become congruent with the outer surface of the second stiff layer during an impact, particularly so as to increase the duration of impact and sliding before contact.
Furthermore, particularly, the first layer can elastically deform and/or plastically deform and/or fracture during impact. Furthermore, the first layer can comprise at least one relief cut and/or at least one structural element to permit deformation.
Further, according to a preferred embodiment of the helmet, the first layer contacts the reactive layer (particularly membrane) merely via a localized portion of the inner surface of the first layer (i.e. said portion comprising an area being smaller than the area of the inner surface of the first stiff layer), wherein particularly said portion is arranged at a perimeter of the first layer.
Further, according to a preferred embodiment of the helmet, said localized portion(s) comprise an increased stiffness compared to an adjacent portion of the first layer, particularly so as to reduce the area of the reactive layer necessary for facilitating relative movement between the first layer and the second layer.
Preferably, the helmet is a cycling helmet. However, the technology of the present invention and variations thereof can be applied to other helmets. Even helmets that are not made via EPS in-moulding but via injection moulding. Particularly, the helmet can also be a motorcycle helmet. For such a helmet, higher impact speeds allow the activation force for facilitating the rolling of the balls of the reactive layer or membrane to be higher. This adds to the durability of the helmet during manufacturing and everyday use

14 Particularly, in an embodiment of the invention, instead of basing the first layer(s) on sheets e.g. formed out of polycarbonate, the first layer(s) and the second layer can be injection molded first and second layers.
The helmet according to one of the preceding claims, wherein the respective first layer is an injection-moulded first layer and/or wherein the second layer is an injection-moulded second layer.
Injection moulding for a helmet such as a motorcycle helmet is afforded by the weight requirements of such helmets being less strict than regarding cycling helmets and by the linear impact.
The helmet according to one of the preceding claims, wherein a portion of an inner surface of the respective first layer is bonded to a portion of an outer surface of the second layer.
Particularly, according to an embodiment, the portion of the inner surface of the respective first layer is bonded to the portion of the outer surface of the second layer by means of a double-sided adhesive tape. Preferably, said portion of the inner surface is an edge portion of the inner surface of the first layer. Further, preferably said portion of the outer surface is an edge portion of the outer surface of the second layer The helmet according to one of the preceding claims, wherein the first layer is connected to the second layer by connectors, the respective connector protruding from an inner surface of the first layer and extending through an associated through-opening of the second layer with an end portion of the connector, the end portion engaging with the second layer (wherein the end potion preferably comprises a nose engaging behind an edge region of the through-opening) to connect the first layer to the second layer, wherein the respective connector is configured to break at said impact threshold to release the first layer from the second layer.
Furthermore, according to a preferred embodiment of the helmet, the first layer is a sacrificial layer configured to smooth out a surface impacting on an outer surface of the first layer of the helmet to allow the balls to roll on the sacrificial layer. Preferably, the sacrificial layer is configured to be completely released from the helmet or partially released from the helmet during an oblique impact and particularly to not translate during said impact relative to the impacting surface (i.e. to stick to the impacting surface). Partially released particularly means that the helmet comprises a structure that still connects the sacrificial layer to the helmet after release, such as e.g. a tether.

15 According to yet another preferred embodiment of the helmet according to the present invention, an energy necessary to release the respective ball is in the range between 0.005 Joules and 0.5 Joule per ball.
The helmet comprises a plurality of first layers, and a reactive layer sandwiched between each first layer and the second layer (and connected to the first and second layers).
Particularly, as described above the respective reactive layer comprises a plurality of rigid balls, that remain rigid during normal use of the helmet and are configured to roll at an impact threshold over an outer surface of the second layer. Furthermore, the respective reactive layer can be a membrane as described above, which will also be detailed further down below.
Furthermore, preferably, the respective first layer and associated reactive layer (or membrane) comprise an elongated shape and are preferably arranged side by side in the direction of the helmet's cross axis and preferably extend along the longitudinal axis of the helmet (i.e. from the back to the front of the helmet), wherein the vertical axis of the helmet is essentially normal to the head of the person wearing the helmet.
the first layers being arranged adjacent one another. Particularly, this means that neighboring first stiff layers comprise edge portions contacting one another Furthermore, each first layer of said plurality of first layers can be configured according to the embodiments described herein with respect to the first layer described above, which will be briefly reiterated further down below.
Preferably, according to an embodiment, the rigid balls are formed from a material comprising a Young's modulus (modulus of elasticity) in the range stated above.
Particularly, according to a preferred embodiment, the balls comprise a diameter in the range stated above.
Furthermore, particularly, the balls are distributed along an inner surface of the respective first layer such that they cover an area that corresponds to 10% to 30%, preferably about 20% of the area of said inner surface of the respective first layer.
Further, preferably, the rigid balls are bonded to a substrate film of the corresponding reactive layer via an adhesive configured to undergo brittle failure. Particularly, the respective substrate film comprises a thickness smaller than 200 pm.

16 Particularly, the respective substrate film comprises an adhesive layer preferably consisting of a pressure sensitive adhesive arranged on a side of the respective substrate film facing away from said plurality of balls.
Furthermore, the respective reactive layer preferably is (or comprises) a membrane bonded to the first and the second layer, wherein the respective membrane comprises the respective substrate film and the respective plurality of balls arranged thereon.
Preferably, as described above, the respective membrane or the substrate film is bonded to the outer surface of the second layer via said adhesive layer consisting of said pressure sensitive adhesive of the respective substrate film.
Furthermore, preferably, the respective membrane or its respective plurality of balls is bonded to the inner surface of the first layer (A surface), particularly during high temperature moulding, via an adhesive layer, preferably an adhesive layer comprising or consisting of a thermo-softening adhesive.
Particularly, as described above, the respective first layer can a sheet (the respective sheet being preferably formed from a plastic material such as polycarbonate (PC)), a color layer (e.g.
a colored ink layer) arranged on an inner surface of the respective sheet, a protective layer arranged on the color layer, wherein said adhesive layer that bonds the respective membrane to the inner surface of the respective first layer is bonded to the respective protective layer.
Particularly, in all embodiments, the inner surface of the respective first layer faces towards the head of said person wearing the helmet.
Furthermore, particularly, the respective protective layer can be a heat resistant ink layer (the heat resistant ink layer can be screen printed or UV printed onto the color layer (e.g. colored ink layer)). Furthermore, alternatively, the respective protective layer can be one of the layers mentioned above. Further, particularly, the respective protective layer can comprise a thickness below 0.1 mm and/or a yield strength larger than 20 MPa. Further, particularly, the respective protective layer can have a thermal expansion differing less than 5 % from a thermal expansion of a material of the respective first layer.
Furthermore, alternatively, the respective first layer that can also be a twin sheet assembly as described above, comprising an outer sheet and an inner sheet (e.g.
thermoformed simultaneously), wherein both sheets preferably consist of polycarbonate (PC), wherein the inner sheet of the respective twin sheet assembly is perforated (see also above).

17 According to yet another preferred embodiment of the present invention, the first layer can be formed by a fabric or comprise a fabric. Particularly, in all embodiments of a helmet according to the present invention, the first layer can be formed or comprise such a fabric.
According to another preferred embodiment of the helmet according to the present invention, the respective first layer and the associated reactive layer (particularly in form of the respective membrane) form a replaceable unit. Particularly, after an oblique impact, the respective membrane, and if still partially connected, the respective first layer, are configured to be removed (e.g. manually) and replaced by a replacement unit comprised of a first layer and a membrane wherein the replacement unit is configured to be connected to the outer surface of the second layer (particularly bonded to the outer surface of the second layer by an adhesive layer). Therefore, a third aspect of the present invention also relates to a replacement unit comprising a first layer and a membrane. The first layer and the membrane can be further characterized as described herein in relation to the method and helmets.
Furthermore, a fourth aspect of the present invention relates to a system comprising a helmet according to the present invention and at least one replacement unit according to the present invention.
According to a fifth aspect of the present invention relating to a helmet, a helmet is disclosed, the helmet comprising a first layer forming an outer surface of the helmet, and a second layer, wherein under an oblique impact, the first layer can move relative to the second layer, wherein particularly the second layer can move under the first layer.
According to a preferred embodiment of the helmet according to the fifth aspect, the first layer comprises an angled edge portion that is arranged on a face side of the second layer (the face side extending in a thickness direction of the second layer) and can thus slide along the face side without being caught on the latter.
Furthermore, according to a preferred embodiment of the helmet according to the fifth aspect, the helmet comprises an energy absorbing layer, the second layer being arranged on the energy absorbing layer.
Furthermore, according to a preferred embodiment of the helmet according to the fifth aspect, the energy absorbing layer comprises a raised boundary portion that ramps up towards a periphery of the energy absorbing layer and provides an outer surface being flush with an outer surface of the angled edge portion of the first layer.
According to yet another preferred embodiment of the helmet according to the fifth aspect, the second layer comprises an edge portion that covers the raised boundary portion which ramps up towards the periphery of the energy absorbing layer, wherein preferably the edge portion of the second layer provides an outer surface being flush with an outer surface of the first layer.

18 Furthermore, the helmet according to the above described fifth aspect of the present invention can comprise a reactive layer sandwiched between the first layer and the second layer as described herein. Particularly, the helmet according to the fifth aspect of the present invention can be further characterized by the features stated in claims 1 to 58, the corresponding embodiments described herein, and all the other features of the helmets described herein.
Furthermore, according to the first aspect of the present invention, a method is disclosed, namely a method for manufacturing a helmet, particularly a helmet for cycling, particularly a helmet according to the present invention as described and claimed herein, wherein the method comprises the steps of:
(a) Providing a first layer and an adhesive layer arranged thereon, (b) Providing a second layer and an adhesive layer arranged thereon, (c) Providing a membrane comprising a plurality of balls bonded to a substrate film of the membrane using an adhesive (the adhesive being preferably configured to undergo brittle failure), the substrate film comprising an adhesive layer on a side facing away from said plurality to balls, (d) Arranging the membrane on an outer side of the second stiff layer and bonding the membrane to the second layer via said adhesive layer of the substrate film (e) Arranging the first layer, the second layer and the membrane in a cavity of a mould, wherein the membrane is arranged between the first and the second layer, and (f) Providing a material in the cavity adjacent the adhesive layer arranged on the second layer and forming an energy absorbing layer of the helmet, wherein the energy absorbing layer is bonded to an inner surface of the second layer via said adhesive layer arranged on the second layer, and bonding the plurality of balls to the first layer via said adhesive layer arranged on the first layer.
Particularly, according to a preferred embodiment of the method, step f) comprises providing a heated material in the cavity adjacent the adhesive layer arranged on the second layer and pressurizing the cavity for forming the energy absorbing layer, wherein the energy absorbing layer is bonded to an inner surface of the second layer via said adhesive layer arranged on the second layer, and bonding the plurality of balls to the first layer via said adhesive layer arranged on the first layer. The heated material can be provided in an embodiment by heating

19 the material in the cavity or by injecting heated, particularly molten, material into the cavity of the mould.
Furthermore, in all embodiments, the second layer can be formed in one piece, but can also be formed by multiple sheets arranged side by side on the energy absorbing layer.
According to a preferred embodiment of the method, the adhesive layer arranged on the first layer is a thermo-softening adhesive layer (step a)), and/or wherein the adhesive layer arranged on the second layer is a thermo-softening adhesive layer (step b)), particularly a binder ink such as acrilux, and/or wherein the adhesive layer of the substrate film comprise a pressure sensitive adhesive.
Particularly, in a preferred embodiment of the method, the material is a bulk material, particularly in the form of pellets, wherein particularly said material is polystyrene (PS), particularly expanded polystyrene (EPS).
Particularly, the material is heated in the cavity by means of super-heated steam, particularly at about 2bar, particularly for a time span of 4 minutes to 5 minutes, which also softens the thermo-softening adhesive layers for bonding the balls to the first layer and the second layer to the energy absorbing layer.
Furthermore, according to a preferred embodiment of the method, providing a first layer in step (a) comprises proving a sheet as a base structure of the first layer, applying a color layer on the sheet (preferably by printing, e.g. screen printing, a colored ink on the sheet), wherein thereafter preferably a light bleed preventing base coat is applied on the color layer, optionally applying a protective layer on the color layer (particularly on the light bleed preventing base coat), wherein particularly the protective layer is one of the layers described above, particularly a cross-linked polymer barrier coat, and wherein arranging said adhesive layer on the first layer comprises arranging said adhesive layer on the protective layer.
Particularly, according to an embodiment of the method the sheet is thermoformed and trimmed to achieve a desired contour of the sheet (or first layer). The sheet can be thermoformed and trimmed after having applied said color layer, particularly light bleed preventing base coat, protective layer and adhesive layer.
Particularly, the sheet of the first layer can be made out of polycarbonate (PC).
Furthermore, according to a preferred embodiment of the method, providing the second layer in step (b) comprises proving a sheet (as a base structure of the second layer), applying a color layer on the sheet of the second layer (preferably by printing, e.g.
screen printing, a

20 colored ink on the sheet), wherein thereafter preferably a light bleed preventing base coat is applied on the color layer, and wherein arranging said adhesive layer on the second layer comprises arranging said adhesive layer on the color layer, particularly on the light bleed preventing base coat.
Particularly, according to an embodiment of the method the sheet of the second layer is thermoformed and trimmed to achieve a desired contour of the sheet (or first layer). The sheet can be thermoformed and trimmed after having applied said color layer, particularly light bleed preventing base coat, protective layer and adhesive layer.
Particularly, the sheet of the second layer can be made out of polycarbonate (PC).
As described above, the helmet can comprise a plurality of first layers. In this case the above described step (a) comprises providing said plurality of first layers (each first layer can be provided as described above with respect to the first layer).
Furthermore, according to a preferred embodiment of the method, step (c) of providing the membrane comprises providing the substrate film by kiss cutting a laminate comprising a top layer and a backing, the substrate film being kiss cut from the top layer resulting in the substrate film arranged on the backing and a surrounding portion of the top layer, wherein particularly the substrate film comprises an elongated shape being adapted to a geometry of a corresponding portion of the outer surface of the second layer.
According to a preferred embodiment of the method, step (c) further comprises:
- removing said surrounding portion (also denoted as negative web), - arranging dots (preferably of a diameter of about 2mm) of said adhesive, particularly in a repeating or desired pattern, onto the substrate film, and - placing a ball of said plurality of balls on each dot of adhesive and curing or letting the adhesive cure to bond the balls to the substrate film.
According to a preferred alternative embodiment of the method, step (c) further comprises:
- applying a layer of said adhesive onto the substrate film, - removing said surrounding portion (also denoted as negative web) before the adhesive has set, and - placing said plurality of balls in a repeating or desired pattern on the layer of said adhesive and curing or letting the adhesive cure to bond the balls to the substrate film.

21 Furthermore, according to a preferred embodiment of the method, the second layer comprises recesses (e.g. at an edge) and/or through-holes through which portions of the material extend upon heating the material and pressurizing the cavity towards the first layer to bond with the first layer via said adhesive layer arranged on the first layer (i.e. through-weld). In an embodiment, the adhesive layer arranged on the first layer is partially or completely omitted and said portions of the material extending through the recesses and/or through-holes bond to the first layer (e.g. without an intermediary separate adhesive layer, see also above). Thus, in step a) and f) described above said adhesive layer may not be used at all or merely for bonding the balls to the first layer.
According to a preferred embodiment, the substrate film is formed out of a polymer, particularly PVC, see also above.
Once cooled, the fully formed helmet body is preferably removed from the cavity, and can have ancillaries added and may then be packaged.
Furthermore, in the method according to the present invention and its embodiments described herein, the balls can be bonded to the outer surface of the second layer (particularly directly) using an adhesive, particularly an adhesive comprising PVA, i.e., the substrate film can be omitted.
Furthermore, in the method according to the present invention and its embodiments described herein the balls (whether via membrane or direct) can be bonded to the outer surface of the second layer B before the outer surface of the second layer is formed into shape.
Furthermore, according to a sixth aspect, the present invention relates to a helmet, particularly a helmet for cycling, according to the features of claim 59.
Particularly, the sixth aspect of the present invention relates to a helmet, particularly a helmet comprising a motion inhibiting layer to reduce negative rotation.
In an impact of a helmet on an object, particularly of a helmet on a street or other kind of terrain in a bicycle accident, the normal component FN of the impact force directed perpendicular from the particular impact location of the object is in general not aligned with the center of mass of a head of a person wearing the helmet. The displacement between the normal force and the center of mass of the head thereby represents a first lever arm vector Li with the product of normal force and the first lever arm causing a first, negative torque of the head. In the absence of other forces, a negative rotation of the head with a negative direction of rotation is induced.

22 However, due to friction or other resistive forces, such as rolling resistance between the object and an outer layer, the outer layer is subject to a tangential friction force, FT. The displacement between the direction of the tangential friction force and the center of mass represents a second lever arm vector L2 with the product of the tangential friction force and the second lever arm vector leading to a second, positive torque to helmet and head. The positive torque is directed opposite to the negative torque caused by the normal component of the impact force and the first lever arm vector.
Depending on the magnitude of the respective torques, upon impact, the head will rotate either positively (along the direction of the friction force) or negatively (opposite to the direction of the friction force).
In both cases, the net rotation of the head upon impact is known to cause severe injuries for the brain and neck of the person.
Typically, helmets in the prior art rotate positively because the resistive forces between the various layers forming the helmet are relatively high. However, recent helmet developments have now reduced resistive forces to a regime that features negative rotation of the helmet upon impact.
It is object of the present invention to provide a helmet with enhanced safety features, particularly with respect to the aforementioned problem of negative rotation that can be manufactured particularly cost efficient. The object is achieved by the device having the features of claim 59.
Advantageous embodiments are described in the corresponding dependent claims.
The invention discloses according to the sixth aspect a helmet for protecting the head of a person upon an impact, the helmet comprising an outer surface, the helmet being configured to reduce negative rotation of a head of the person wearing the helmet resulting from an impact force acting on the outer surface of the helmet upon said impact.
As stated above, the negative rotation of the head is directed along the negative torque caused by the normal component of the impact force and the first lever arm vector corresponding to the displacement between the normal component of the impact force and the center of mass. As such, the negative rotation is directed opposite of the positive torque created by the cross product of the tangential friction force acting on the outer surface upon impact and the second lever arm vector extending parallel to the normal component of the impact force to the center of mass. In the context of the present invention, the term 'center of

23 mass' refers to a center of mass of the helmet and a person wearing the helmet, particularly the center of mass of the helmet and a head of a person wearing the helmet.
While helmet in the prior art typically feature positive rotation due to the relatively high friction between the outer surface of the helmet and the head of the person, application of sufficiently low friction layers may result in negative rotation. Since any kind of rotation is harmful for head and neck of the person, the present invention proposes to introduce at least one motion inhibiting element to the helmet in order to reduce the rotation of the helmet, particularly the negative rotation.
According to an embodiment of the sixth aspect of the present invention, the helmet may further comprise an inner layer and at least one outer protective layer wherein for reducing a positive rotation of the head of the person wearing the helmet upon impact, the at least one outer protective layer may be configured to move relative to the inner layer.
Preferably, said inner layer may comprise energy absorbing elements and/or an energy absorbing material, so as to form an energy absorbing layer.
In case the motion between the inner layer and the at least one outer protective layer is characterized by a sufficiently low friction to result in negative rotation of the helmet, the motion inhibiting elements may be configured to reduce a negative rotation of the helmet.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting elements may be used to introduce an additional amount of friction to the helmet, particularly to the inner layer and the at least one outer protective layer, so as to advantageously reduce a negative rotation of the helmet, providing protection for the head and neck of the person wearing the helmet.
The motion inhibiting elements are preferably adapted such that the negative torque counteracts the positive torque such that upon impact, the head and helmet experience an angular velocity in the range from -15 rad/s to +15 rad/s, preferably -10 rad/s to +10 rad/s, more preferably -5 rad/s to +5 rad/s.
According to an embodiment of the sixth aspect of the present invention, the motion inhibiting elements may be arranged between the inner layer and the at least one outer protective layer. In this embodiment, the inhibiting layer may advantageously interact with both the inner layer and the at least one outer protective layer so as to control the amount of friction between the inner layer and the at least one outer protective layer, thereby reducing the negative rotation of the helmet upon an impact force.
To this end, the motion inhibiting elements may also comprise or be a motion inhibiting layer.

24 According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may be integrally formed with the inner layer and/or the at least one outer protective layer. Forming the motion inhibiting layer integrally with the inner layer and/or the at least one outer protective layer advantageously contributes to reduce fabrication costs and -time of the helmet.
According to another embodiment of the sixth aspect present invention, the motion inhibiting layer may be configured to deform upon the impact force. Particularly, the deformation of the motion inhibiting layer may for example be a compression or a stretching accompanied by corresponding compression- or shearing forces that may be used to counteract the negative rotation of the helmet.
According to another embodiment of the sixth aspect of the present invention, the helmet may additionally comprise an intermediate layer arranged between the inner layer and the at least one outer protective layer, said intermediate layer being configured to promote the relative motion between the inner layer and the at least one outer protective layer. In particular, the intermediate layer may be a low friction layer comprising interfaces to the inner layer and the at least one outer protective layer with friction coefficient, rolling resistance coefficients and the like that are low enough to cause a net negative rotation of the helmet upon impact. Depending on the choice of the intermediate layer, the motion inhibiting layer may be adapted to compensate the resulting net friction force between the various layers so as to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer comprises a flexible layer, particularly a fabric or a webbing arranged between the motion inhibiting layer and at least one of the following: the inner layer, the intermediate layer, the at least one outer protective layer. The compression or shearing forces caused within the flexible layer upon impact may be used to counteract the relative motion between the inner layer and the at least one outer protective layer and particularly the negative rotation of the helmet. The motion inhibiting layer may alternatively comprise flexible interfaces arranged between the motion inhibiting layer and at least one of the following: the inner layer, the intermediate layer, the at least one outer protective layer.
According to another embodiment of the sixth aspect of the present invention, at least one of the following may comprise a plurality of stacked sub-layers: the inner layer, the at least one outer protective layer, the motion inhibiting layer, the intermediate layer.
The aforementioned layers may alternatively or additionally also comprise multiple mutually connected shell

25 segments that are arranged essentially in a respective plane extending along the respective layer.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may be arranged at least partially within the intermediate layer. As such, the inhibiting layer introducing additional friction may directly interact with the intermediate layer used to reduce the friction, so as to fine tuning the resulting net friction, particularly the net friction between the inner layer and the at least one outer protective layer.
According to another embodiment of the sixth aspect of the present invention, the intermediate layer may be integrally formed with at least one of the following: the inner layer, the motion inhibiting layer, the at least one outer protective layer. Forming the motion inhibiting layer integrally with the inner layer and/or the at least one outer protective layer advantageously contributes to reduce fabrication costs and -time of the helmet.
According to another embodiment of the sixth aspect of the present invention, the intermediate layer and/or the motion inhibiting layer may comprise rollable elements, said rollable elements being configured to promote the motion of the inner layer relative to the at least one outer protecting layer upon the impact force. Particularly, the rollable elements may be for example rolls, beads and the like. The rollable elements may for example comprise a circular diameter between 0.1 mm and 4 mm, particularly between 1 mm and 2 mm, wherein the circular diameter refers to a circular cross-section of the rollable elements. The rollable elements advantageously contribute to a substantially lower friction force and rolling resistance between the intermediate layer and the inner layer and/or the at least one outer protective layer. Depending on the choice of the rollable elements, the motion inhibiting layer may be adapted to compensate the resulting net friction force between the various layers so as to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
Additionally, the intermediate layer and/or the motion inhibiting layer may comprise breaking elements configured to fail upon the impact force, enabling the rollable elements to interact with the inner layer and the at least one outer protective layer, so as to promote the motion of the inner layer relative to the at least one outer protecting layer.
According to another embodiment of the sixth aspect of the present invention, together with the inner layer and the at least one outer protective layer, the motion inhibiting layer may delimit at least one volume, so as to confine at least a fraction of the rollable elements in the at least one volume. As such, also several volumes, particularly with a different number and/or different geometries of rollable elements may be used to finetune the resulting net

26 friction between the various layers, particularly between the inner layer and the at least one outer protection layer upon impact.
According to another embodiment of the sixth aspect of the present invention, the rollable elements, the inner layer, the intermediate layer, the at least one outer protective layer and the motion inhibiting layer may comprise a lower or a larger stiffness, wherein the stiffness of the rollable elements is lower or larger than the stiffness of at least one of the following: the inner layer, the intermediate layer, the at least one outer protective layer, the motion inhibiting layer. By choosing different stiffnesses between the rollable elements and the various layers, the friction between the various layers, particularly the rolling resistance may be controlled, so as to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation. For example, the rollable elements may comprise a larger stiffness than at least one of the various layers mentioned above.
Alternatively, the rollable elements may also comprise a lower elasticity than at least one of the various layers mentioned above. The difference in elasticity thereby represents a parameter to vary the rolling resistance. For example, the lower elasticity may correspond to a young's modulus of less than 3 GPa.
For example, a rolling resistance coefficient between the intermediate layer, particularly the intermediate layer comprising rollable elements, and the at least one outer protective layer and/or the inner layer may be below 0.2.
Optionally, a coefficient of friction between the motion inhibiting layer and the intermediate layer, particularly the intermediate layer comprising rollable elements, or the at least one outer protective layer or the inner layer may differ from a coefficient of friction between the intermediate layer and the at least one outer protective layer or the inner layer. As such, the motion inhibiting layer may preferably be used to introduce an amount of friction into the helmet comprising the various layers mentioned above.
For example, a coefficient of friction between the intermediate layer or the motion inhibiting layer and the at least one outer protective layer or the inner layer may be below 0.8.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may comprise a viscous fluid or a gel. The viscous fluid and/or gel may preferably be configured to introduce a shear stress to the various layers mentioned above, particularly a shear stress between the inner layer and the at least one outer protective layer.
The viscous fluid or gel may preferably be used in combination with the intermediate layer, particularly a low friction intermediate layer optionally comprising rollable elements, wherein the viscous fluid or gel may be chosen such that the interplay of the viscosity creating

27 additional shear stress and the intermediate layer reducing the friction results in a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation. Preferably, the viscous fluid and/or the gel may be arranged in a leak tight volume enclosed by at least the inner layer and the outer protective layer so as to retain the viscous fluid or gel.
For example, the viscous fluid or the gel may comprise a viscosity within 0.001 and 10 Pa s.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may comprise a non-Newtonian fluid or gel. As such, the viscosity of the fluid or gel may depend on the shear stress, which may advantageously be used as another parameter to finetune the interplay of the fluid or gel creating additional shear stress and the intermediate layer reducing the friction, so as to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may comprise motion inhibiting elements. The motion inhibiting elements are preferably configured to inhibit the relative motion between the inner layer and the at least one outer protective layer. The motion inhibiting elements may advantageously be used in combination with the intermediate layer, particularly with the intermediate layer comprising rollable elements, so as to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
To this end, individual motion inhibiting elements forming the motion inhibiting elements may be configured to rupture upon the impact force. To this end, a geometrical feature, particularly a diameter, a width or a length of an individual inhibiting element may be indicative for an individual rupture force required to rupture an individual inhibiting element, wherein the rupture force counteracts the negative rotation of the helmet upon the impact force.
For example, the motion inhibiting elements may cover less than 80% of a total lateral surface area defined by the at least one outer protective layer.
The motion inhibiting elements may for example be formed as at least one of the following: a cylinder, a cone, a pyramid, a cuboid, a truncated cone.
Optionally, the motion inhibiting elements may contact the at least one outer protective layer and the inner layer via a lateral contact surface area, wherein a ratio of the lateral contact surface area and the total lateral surface area is for example within 0.05 and 0.5.

28 According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may comprise a connector or a plurality of connectors being integrally formed between at least two of the following: the inner layer, the intermediate layer, the at least one outer protective layer.
Said connector or connectors may be configured to deform and/or to rupture simultaneously and/or sequentially upon the impact force, so as to counteract the negative rotation of the helmet. The connectors may preferably be used in combination with the intermediate layer, particularly the intermediate layer comprising rollable elements, wherein the choice of connectors introducing friction and the intermediate layer reducing friction may be adapted to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
To this end, individual connectors forming the plurality of connectors may comprise individual rupture forces, wherein the individual rupture forces take on at least two values. As such, a plurality of individual connectors with tailored deformation or rupturing properties may be used within the motion inhibiting layer to achieve a minimum net rotation of the helmet upon impact, particularly a minimum negative rotation.
For example, the connectors may comprise or be an adhesive, a thermoplastic, an elastomer, a ceramic or a metal.
Preferably, the connectors may have a different elasticity than the inner layer and/or the at least one outer protective layer. The difference in elasticity between the connectors and the inner layer and/or the at least one outer protective layer may advantageously be used to vary the friction and/or the rolling resistance between the connectors and the inner layer and/or the at least one outer protective layer.
Again, referring to the motion inhibiting layer, the motion inhibiting layer may comprise at least one of the following: a plastic material, an elastic material, a polymer, a metal.
According to another embodiment of the sixth aspect of the present invention, the motion inhibiting layer may be configured such that the reduction of negative rotation of the helmet depends on a direction of the impact force. To this end, for example a plurality of said connectors or inhibiting elements, particularly comprising different individual rupturing forces may be used.
As such, the motion inhibiting layer may be configured such that the reduction of negative rotation upon an impact force resulting in a rotation of the helmet around a first axis is larger

29 than the reduction of negative rotation upon an impact force resulting in a rotation of the helmet around a second axis.
For example, the first axis may run through a coronal plane within a head of a person wearing the helmet and the second axis may run through a sagittal plane within the head of the person wearing the helmet. Since most impacts induce a stronger (negative) rotation of the head and helmet around an axis through the coronal plane compared to the sagittal plane, this choice of the first axis and the second axis may advantageously contribute to reduce a net rotation of the helmet, particularly a negative rotation.
Preferably, the motion inhibiting layer may be configured to limit the motion of the inner layer relative to the at least one outer protective layer upon the impact force to an absolute rotational velocity of less than 15 rad/s, wherein the rotational velocity may be positive or negative.
According to yet another embodiment of the sixth aspect of the present invention, at least two of the following may be configured to geometrically and/or mechanically lock so as to reduce the negative rotation upon impact: the inner layer, the intermediate layer, the motion inhibiting layer, the outer protective layer. To this end, the inner layer, the intermediate layer, the motion inhibiting layer and/or the outer protective layer may comprise geometrical features that promote a geometrical locking between at least two of these layers, for example pairwise interlocking segments of each of the at least two layers which engage upon impact and the like.
According to another embodiment of the sixth aspect of the present invention, in the absence of the motion inhibiting elements or the motion inhibiting layer, upon impact, the helmet would experience negative rotation, or exceed a pre-defined positive threshold of positive rotation.
Particularly, exemplary embodiments of aspects of the present invention are described below in conjunction with the Figures. The Figures are appended to the claims and are accompanied by text explaining individual features of the shown aspects of the present invention and their embodiments. Each individual feature shown in the Figures and/or mentioned in the text of the Figures may be incorporated (also in an isolated fashion) into a claim relating to the device according to the present invention. Furthermore, the features disclosed in conjunction with a specific aspect can be combined with embodiments of other aspects of the present invention in every sensible way.
In the following, exemplary embodiments as well as further features and advantages of the present invention are described below with reference to the Figures, wherein

30 Fig. 1 shows an embodiment of the helmet according to the present invention, Fig. 2 shows an alternative embodiment of the detail shown in Fig. 1, Fig. 3 shows a cross-sectional view of an embodiment of the helmet according to the present invention, wherein the respective first layer comprises a front portion being embedded in the energy absorbing layer of the helmet, Fig. 4 shows details of two embodiments of a helmet according to the present invention, wherein here a protective layer is provided for preventing an excessive indentation of the balls of the reactive layer into the color layer of the first layer of the helmet, wherein (A) and (C) show the situation before applying heat and pressure in the cavity of a mould, and (B) and (D) shows the situation after moulding of the helmet with the balls embedded into the adhesive layer, but prevented from further intrusion by the respective protective layer ((A) and (B): protective layer on top of color layer; (C) and (D):
protective layer formed by lower sheet of a twin sheet assembly), Fig. 5 shows an embodiment of kiss cutting the substrate film for carrying the ball of reactive the layer/membrane, Fig. 6 shows an embodiment of bonding the reactive layer/membrane to the outer surface of the second layer of the helmet, Fig. 7 shows an embodiment of the helmet according to the present invention, wherein two adjacent first layers of the helmet each comprise a chamfer at the opposing edges toward mutual locking up of said first layers went said first layers move relative to one another, Fig. 8 shows an embodiment of the helmet according to the present invention, wherein the first layer is connected to the second layer of the helmet by means of connectors extending from the first layer to the second layer, Fig. 9 shows an embodiment of the helmet according to the present invention allowing the initiating of the reactive layer of the helmet by means of a buckling feature upon an impact, Fig. 10 shows an embodiment of the helmet according to the present invention allowing lifting an edge portion of a first layer by means of a buckling feature of the first layer upon impact,

31 Fig. 11 shows an embodiment of the helmet according to the present invention allowing pivoting of the helmet upon impact, Fig. 12 shows an embodiment of the helmet according to the present invention allowing release of the first layer in a desired direction due to a deformation of the first layer upon impact, Fig. 13 shows an embodiment of the helmet, wherein the first layer is configured so as to achieve altering the direction of normal forces on the helmet to alter the moment caused by the center of mass of the system comprises of the helmet and the head wearing the helmet, Fig. 14 shows an embodiment of the helmet according to the present invention allowing the reduction of transmission of radial forces from the first layer to the second layer where the two layers meet, Fig. 15 shows an alternative embodiment for the reduction of said radial force, and Fig. 16 shows an embodiment of a helmet having a chamfered or rounded edge portion to prevent an edge of the first layer from becoming caught on said edge portion.
Fig. 17 shows a schematic of the relevant forces and lever arm vectors corresponding to positive and negative torque of a helmet upon impact on an object.
Fig. 18a-c shows various impact scenarios of a person wearing a helmet impacting on an object, wherein the resulting forces cause a positive rotation of the head and helmet (scenario Fig. 18c), a negative rotation of the head and helmet (scenario Fig. 18b) and the ideal case of zero rotation (scenario Fig. 18a).
Fig. 19a shows an embodiment of the helmet according to the sixth aspect of the present invention, comprising at least one outer protective layer, a motion inhibiting layer and an inner layer.
Fig. 19b shows various motion inhibiting elements of the motion inhibiting layer.
Fig. 20 shows an embodiment of the helmet according to the sixth aspect of the present invention, wherein the at least one outer protective layer is integrally formed with the motion inhibiting layer.
Fig. 21 shows an embodiment of the helmet according to the sixth aspect of the present invention, comprising a fluid or gel.

32 Fig. 22 shows an embodiment of the helmet according to the sixth aspect of the present invention, comprising a flexible layer.
Fig. 23 shows an embodiment of the helmet according to the sixth aspect of the present invention, comprising at least one connector.
Fig. 1 shows an embodiment of a helmet 1 according to the present invention.
According thereto, the helmet comprises at least one first layer 10, preferably a plurality of first layers forming an outer surface of the helmet 1 on which an impact, particularly oblique impact may occur, i.e., an impact having a force component running tangentially with respect to said outer surface.
The helmet 1 further comprises a second layer 30, and reactive layers 20, each reactive layer being sandwiched between an associated first layer 10 and the second layer 30.
In case the helmet comprises a single first layer 10, the helmet can comprise just a single reactive layer underneath it. In the following, the invention will be described in the context of multiple first layers 10. As shown in Fig. 1 the first layers 10 preferably comprise a longitudinal shape and 15 extend along the longitudinal axis X of the helmet 1. Furthermore, preferably, the first layers 10 are arranged side by side in the direction of the cross axis Y of the helmet 1. Further, the first layers 10 are preferably configured as stiff first layers 10 which can be achieved by selecting an appropriate material for the first layers 10 and geometry during the curved shape of the first layers 10 contributes to said stiffness. Particularly the first layers 10 can be formed 20 out of polycarbonate and can comprise a thickness in the range from 0.25 mm to 20 mm, preferably 0.4 to 1 mm. Furthermore, the first layers 10 can each comprise a curvature in the direction of the longitudinal axis X as well as in the direction of the cross axis Y. Other materials for the first layers are also conceivable. Likewise, as the first layers 10, the second layer 30 being arranged beneath the first layers 10 is also preferably adapted to be stiff in the sense described above. Furthermore, the second layer 30 is arranged on an energy absorbing layer 40 configured to absorb energy of an impact on the helmet 1 particularly in a normal direction of the outer surface of the helmet (e.g. along the vertical axis of the helmet). The energy absorbing layer 40 can be formed out of an expanded polystyrene foam (EPS) and can be bonded to an inner surface 30b of the second layer by an adhesive layer (33) (e.g. acrilux or other suitable therm 0-softening adhesives) The second layer 20 preferably comprise a thickness in the range from 0.25 mm to 20 mm and may also be formed out of polycarbonate. As shown in Fig. 1, the helmet may comprise through-openings 8 extending through the layers 10, 20, 40 for allowing venting of the head of a person wearing the helmet 1. Such through-openings 8 may by flanked by first layers 10 on either side of the respective through-opening.

33 Preferably, the respective reactive layer 20 comprises a plurality of balls 2 (e.g. in the form of preferably rigid spherical bodies) that remain rigid during normal use of the helmet 1 (when no impact occurs) and are configured to roll at an impact threshold over an outer surface 30a of the second layer 30 (also denoted as B surface).
The impact threshold corresponds to a pre-defined tangential force on a first layer 10 that, if exceeded upon an oblique impact, caused the balls 2 to roll. In a preferred embodiment, the balls comprise a diameter of about 2 mm. Further, the balls can comprise the packing density described herein. Preferably, the respective reactive layer 20 is configured to hold the respective first layer 10 such that a tangential force required to activate rolling of the balls 2 of the reactive layer is about 0.1kN (or higher).
Preferably, as indicated in Fig. 1 the respective reactive layer 20 (Fig. 1 shows only one such reactive layer 20, but such a reactive layer 20 is present under each first layer 10) is formed as a membrane 20 that comprises the balls 2 and can be handled in a convenient fashion during production of the helmet 1.
Particularly, as indicated in the details of Fig. 1 and 2, the respective membrane 20 comprises a substrate film 21 and a plurality of balls 2 arranged thereon. Particularly, the balls 2 are bonded to the substrate film 21 via an adhesive 22 that is preferably configured to undergo brittle failure to allow the balls to roll on the substrate 21 / over the second layer 30 when said impact threshold is exceeded. Preferably, the substrate film 21 comprises a thickness smaller than 200 pm and can be formed out of a polymer such as PVC. Other materials are also conceivable. Furthermore, the substrate film 21 can comprises an adhesive layer 23 such as a pressure sensitive adhesive (PSA) arranged on a side of the substrate film 21 facing away from the balls 2. This allows one to easily place the membrane on the second layer 30 as shown in Fig. 6 either manually or automatically (e.g. by means of a suitable machine) and bond the respective membrane 20 with the balls 2 therein to the second layer 30.
Furthermore, the membrane 20 can be bonded to the inner surface 10a of the respective first layer 10 by an adhesive layer 14 applied to the respective first layer 10 that bonds to the balls 2 of the respective membrane 20, e.g. during forming of the energy absorbing layer 40. For this, the adhesive layer 14 can comprise a thermo-softening adhesive.
Furthermore, as shown in Fig. 4, the respective first layer 10 is preferably formed in a manner that prevents an excessive indentation of the balls 2 into the thermo-softening adhesive layer 14 during production. For this, as shown in Fig. 4 (A) and (B), the respective first layer 10 comprises a sheet 11 being preferably formed from a plastic material such as polycarbonate (PC), at least one color layer 12 (e.g. a colored ink layer) arranged on an inner surface of the

34 sheet 11, optionally a light bleed preventing base coat applied to the at least one color layer 12, and a protective layer 13 arranged on the color layer 12 (or base coat), wherein said adhesive layer 14 that bonds the membrane 20/balls 2 to the inner surface 10a of the first layer is arranged on the protective layer 13. The protective layer 13 now achieves that during 5 forming of the helmet 1 in a mould, the balls 2 do not intrude through the heated soft adhesive layer 14 into the color layer 12, but are prevented from doing so by the protective layer 13 (cf.
Fig 13(B)). This also prevents that the balls 2 are visible from the outside in case a transparent material is used for the sheet 11. The protective layer 13 can e.g. be formed out of the materials stated above and preferably comprises a thickness below 0.1 mm and/or a yield strength larger 10 than 20 M Pa.
Alternatively, as shown in Fig. 4 (C) and (D), the first layer 10 can be a twin sheet assembly comprising an outer sheet 11 and an inner sheet 110 that can be thermoformed simultaneously, wherein both sheets 11, 110 preferably consist of polycarbonate. Here, at least one color layer 12 (particularly a colored ink layer) and an adhesive layer 140 (particularly an adhesive ink layer) are arranged between the outer and the inner sheet 11, 110, the adhesive layer 140 bonding the inner sheet 110 to the outer sheet via the at least one color layer 12.
The penetration barrier for the balls 2 is now formed by the inner sheet 110, i.e., in the mould the balls 2 can indent the softened adhesive layer 14, but are prevented from intruding further layers by the inner sheet 110 (cf. Fig. 4 (D)) which thus forms a protection layer of the first layer 10.
Furthermore, as indicated in the details of Figs 1, 2 and in Fig. 7, the helmet 1 preferably comprises ramp features that cause the respective first layer 10 to bend away from the second layer 30 to avoid butting up of the first layer 10 on a portion of the helmet 1, particularly on second layer 30 or a neighboring first layer 10 or another structure.
As shown in the detail of Fig. 1, the first layer 10 comprises an angled edge portion 10b that is arranged on a thin face side 30c of the second layer 30 and can thus slide along the face side 30c without being caught by the latter. Furthermore, preferably, the energy absorbing layer 40 comprises a raised boundary portion 40a that ramps up towards the periphery of the energy absorbing layer 40 and provides an outer surface 40b being flush with an outer surface 10c of the angled edge portion 10b of the adjacent first layer 10. The angled edge portion 10b can also have a round transition to an adjacent portion of the first layer 10.
In the modification of this edge termination shown in Fig. 2, the second layer 30 comprises an edge portion 30d that covers the raised boundary portion 40a that ramps up towards the periphery of the energy absorbing layer 40. Here, the edge portion 30d of the second layer 30

35 provides an outer surface 30e being flush with the outer surface 10c of the adjacent first layer 10.
Furthermore, as indicated in Fig. 7, the helmet 1 can comprise two adjacent first layers 10, wherein the two first layers 10 preferably comprise adjacent edges 10d, wherein each edge 10d preferably comprises a chamfer 10e allowing an obliquely impacted first layer 10 to move more easily on top of a neighboring first layer 10 without becoming entangled with the adjacent first layer 10. Alternatively, or in addition, the second layer 30 may comprise a ramp region 9, e.g. in form of a recess or indentation, below the edges 10d of the adjacent first layers 10 thus allowing an edge 10d of an obliquely impacted first layer to be lifted upwards and travel over the respective adjacent first layer 10 and its edge 10d.
Furthermore, as shown in Fig. 16, the energy absorbing layer 40 and/or the second layer 30 can comprises an edge portion 80 having a chamfered or rounded edge 80a to prevent a trailing edge 10g of the first layer 10 from becoming caught on said edge portion 80 when moving relative to the second layer and/or energy absorbing layer over said edge portion 80 after an oblique impact that causes relative movement of the first layer in direction D3 with respect to the second layer 30 / energy absorbing layer 40. Fig. 16 (A) shows the situation before an impact, and Fig. 16 (B) shows the relative movement between first and second layer 10, 30 after an oblique impact. Said edge 10g is also denoted as trailing edge with respect to direction 03. Furthermore, on an inner surface of the first layer 10, the first layer 10 can comprise a fillet 81 for allowing the edge 10g to smoothly travel over the edge portion 80.
Furthermore, for certain impact directions the first layer 10 may move towards the face of a person wearing the helmet 1 (e.g. in the direction of the longitudinal axis X
and downwards following the curvature of the second layer 30, cf. Fig. 1). To avoid such a situation, the respective first layer 10 (or at least some of the first layers 10) comprises a front portion 101 as shown in Fig. 3 that is embedded in the energy absorbing layer 40 so that the front portion 101 of the first layer 10 remain in place during an oblique impact in a first direction D1 from a rear of the helmet 1 towards the front of the helmet 1, while a remaining portion 102 of the first layer 10 being connected to the front portion 101 is separated from the second layer 30 and may fold over itself as indicated by the solid arrow. However, during an oblique impact in a second direction D2 from the front of the helmet 1 towards the rear from the helmet 1, said front portion 101 can be allowed to disengage from the energy absorbing layer 40 (and from the helmet) so that it becomes completely separated from the helmet 1.
Alternatively, the remaining portion 102 of the first layer 10 can be configured to tear apart from the front portion of the first layer 10, for instance along a predetermined breaking point.

36 Particularly, front portion 102 can be a tab 102 comprising an opening 103, the tab 102 being embedded in a front portion of the energy absorbing layer 40, such that a portion 400 of the energy absorbing layer 40 extends through said opening 103 such holding the tab 102 in place upon said oblique impact in the first direction Dl. The portion 400 can be configured to break to release the tab 102 upon said oblique impact in the second direction D2.
Alternatively, the remaining portion 102 of the first layer 10 may break away from the tab 102 (e.g. at a predetermined breaking point, see above). Particularly, the front part / tab 101 can have a thinner cross section as the remaining portion 102 of the first layer 10.
Furthermore, as shown in Fig. 14, the first layers 10 of the helmet preferably comprise edge terminations, i.e., edge regions 10b that are configured to reduce a transfer of a radial force FR
from the first layer 10 to the second layer (30) (e.g. acting on the respective first layer 10 upon an impact). In other words, areas where inner and outer layers 10, 30 meet, shall preferably inhibit the transfer of the radial force. If an impact were to happen at this point and load was taken by the joint rather than the adjacent balls 2, a relative movement between the layers would be restricted proportionally to the magnitude of load upheld by the joint. Therefore, the respective edge region 10b can be an angled edge region 10b that extends at an angle x with respect to a normal N of an outer surface 30a of the second layer 30, wherein said angle x is preferably in the range from 20 to 80 , preferably 30 to 70 , preferably 40 to 60 , preferably 40 to 500. Particularly, cos(x) determines the magnitude of transmissible load (for given material properties). If the angle x is too small, a significant portion of the impact force is transmitted directly to the second layer 30 instead of the reactive layer 20, creating high friction.
If on the other side, the angle x is too big, the majority of the force is transmitted to the reactive layer 20 allowing it to move relative to the second layer 30.
Alternatively, as shown in Fig. 15 the respective first layer 10 can comprises an edge region 10b that is connected to the outer surface 30a of the second layer 30 by a compressible intermediary layer 4, particularly to inhibit said transfer of a radial force FR acting on the first layer 10 from the first layer 10 to the second layer 30. For instance, the intermediary layer 4 can be a foam tape or other media that yields readily.
Furthermore, Fig. 9 shows an embodiment of a helmet 1 according to the present invention, wherein here the respective first layer 10 is configured to deform during an impact such that a free movement of the first layer 10 is inhibited during impact, wherein particularly said deformation causes a peeling of the adhesive 22 bonding the balls 2 to the outer surface 30a of the second layer 30 (e.g. via said substrate film 21 and its adhesive layer 23).
As shown in the sequence (A) to (D) of Fig. 9, upon an oblique impact, the convex buckle 5 is configured to flatten and increase in width resulting in a translational movement of a boundary

37 region 50 of the buckle causing the balls 2 to roll. This is a further form of initiating the reactive layer 20. As the first layer 10 deforms it initiates the reactive layer 20 because a downward force causes a translational movement that then causes balls to roll.
Furthermore, this mechanism increases a duration at which the reactive layer 20 can operate.
As the first layer 10 deforms it can also move relative to the second layer 30. This increases the time at which the reactive layer 20 is working. Thus, less reactive layer 20 may be needed which means less weight. Furthermore, due to the buckle 5 exposure of the second layer 30 can be prevented. As the first layer 10 deforms and the buckle 5 flattens, its width increases which helps to reduce the exposure between adjacent first layers 10.
Furthermore, Fig. 10 shows a variant of the buckle 5 of the respective first layer 10, wherein here the buckle 5 is configured to deform on impact to prevent geometric locking of the respective first layer 10 due to becoming entangled with an adjacent structure of the helmet 1.
Therefore, the buckle 5 is adapted so as to cause an edge region 51 of the respective first layer 10 to lift up upon impact on the buckle 5. Due to the raised edge region 51, the risk of butting of the edge region 51 against edges of neighboring structures is significantly reduced.
Thus, geometric locking is prevented due to a peeling motion which differs from the shearing motion which may occur without buckle 5.
Particularly, the respective first layer 10 comprises at least one buckle 5 for supporting said pivoting. Particularly The buckling 5 can have a round shape or a wedge shape As shown in Fig. 11, a buckle 5 provided on the respective first layer 10 can also be utilized to pivot the helmet 1 upon impact so as to reduce a rotational motion of a head of a person wearing the helmet. Particularly, the buckle 5 can have a wedge shape and is made stiff so as to not deform on impact but initiate rotation of the helmet 1 and head about the contact point between the tip of the buckle and the impacting surface.
Furthermore, as indicated in Fig. 12, the buckle 5 may also be utilized to achieve a release in a specific direction. As the first layer stores energy e.g. by having the buckle deformed on impact, it may release it in a particular direction that could be beneficial in controlling motion to the head Furthermore, as shown in Fig. 13, the buckle 5 can be adapted in shape so as to achieve a redirection of a normal force Ni of an impact acting on the first layer 10 such that the redirected normal force Ni comprises a distance A to the center of mass C of the system comprised of the helmet 1 and the head of a person wearing the helmet 1 which introduces a non-zero lever arm A acting against rotation of the helmet upon the oblique impact on buckle 5.

38 As shown in Fig. 13, without the buckle 5, the lever arm in Ni is zero as it goes straight through the center of mass C. With the deformable wedge-shaped buckle 5 the lever arm in N2 is A, which is the perpendicular distance between the center of mass C and N2.
In the embodiments described above, the respective first layer 10 is e.g.
connected to the second layer 30 by means of adhesives. However, in addition or alternatively, the respective first layer 10 may also be connected to the second layer 30 by means of connectors 6 as shown in Fig. 8. The respective connector 6 can protrude from the inner surface 10a of the respective first layer 10 and extend through an associated through-opening 300 of the second layer 30 with an end portion 60 of the connector 6, wherein the end portion 60 engaging with the second layer 30 for connecting the first layer 10 to the second layer 20.
Particularly, the end potion 60 can comprise a nose 61 that is configured to engage behind an edge region 301 of the through-opening 300 to connect the first layer 10 to the second layer 30. Further, the connector 6 is configured to break at a defined impact threshold to release the first layer 10 from the second layer 30, and allow rolling of the balls 2 in particular.
In order to manufacture the helmet 1 as shown in Fig. 1 according to an embodiment of the method of the present invention, the first layers 10, second layer(s) 30 and the intermediary reactive layer 20 may be provide as follows.
Particularly, for providing the second layer 30, flat sheets 31 can be screen printed on an inner surface with a colored ink 32, a light bleed preventing base coat, particularly a protective layer, and a binder ink (adhesive layer) 33 designed to bond the second layer 30 to an energy absorbing layer 40 (e.g. out of EPS) during in-moulding. Particularly, the flat sheets 31 are thermoformed and trimmed (e.g. to conform to the desired shape of the helmet 1).
Similarly, for providing the first layers 10, flat sheets 11 can be screen printed on an inner surface with a colored ink 12, a light bleed preventing base coat, a cross-linked polymer barrier coat (protective layer) 13 to prevent the balls 2 from being visible from the outside, and a thermo-softening binder ink (adhesive layer) 14, specially formulated to bond the first layer 10 to the balls 2. The flat sheets are thermoformed and trimmed (e.g. to conform to the desired shape of the helmet 1).
Furthermore, in order to provide the respective reactive layer / membrane 20, substrate films 21 (e.g. out of PVC) are kiss cut into strips that follow the geometry of the second layer 30 as shown in Figs. 5 and 6.
Particularly, as shown in Fig. 5, providing the substrate films 21 comprises kiss cutting a laminate 7 (e.g. with a tool 3) comprising a top layer 70 and a backing 71, the substrate films 21 being kiss cut from the top layer 70 resulting in the substrate films 21 arranged on the

39 backing 71 and a surrounding portion 72 (so called negative web). This negative web 72 is removed and the substrate films 21 are indexed with small -2 mm dots of adhesive 22 that are applied to the substrate films 21 in a repeating pattern. The balls 2 are placed in each dot of adhesive 22. The adhesive cures/is cured, bonding the balls 2 to the substrate films 21.
The manufactured membranes 20 are applied like a decal to the outer surface 30a of the second layer 30, indexing it to details and edges of the surface 30a Then both the first layers 10 and the second layer 30 are placed inside a cavity of a mould of an in-moulding machine. The helmet is formed via EPS backfilling, which yield the energy absorbing layer 40. The combination of temperature, pressure and particularly moisture (to better conduct heat) causes the ball binding ink 14 to bond to the balls 2 and connect the first layers 10 to the second layer 30 and membrane sub-assembly 20, and further causes the EPS
binder ink 33 on the inside 30b of the second layer 30 to bond the second layer 30 to the energy absorbing layer 40.
Once cooled, the fully formed helmet body is removed from the in-moulding machine, has ancillaries added and is packaged.
Alternatively, instead of applying dots of adhesive 22, a layer of said adhesive 22 can be applied onto the substrate film 21. Then the negative web 72 is removed before the adhesive 22 has set, and the balls 2 are placed in the desired pattern on the layer of said adhesive 22.
The adhesive is then cured or allowed to cure to bond the balls 2 to the substrate film 21.
Fig. 17 demonstrates the problem of rotational forces on a head and/or a neck of a person occurring upon an impact. Generally, the impact of a helmet B100 on an object, particularly of a helmet B100 on a street or other kinds of terrain in a bicycle crash causes a normal component EN of the impact force directed perpendicular from the particular impact location of the object. In the example shown in Fig. 17, the object is represented by an oblique plane with the helmet B100 impacting vertically downwards, resulting in an oblique impact. As shown here, the normal force is in general not aligned with a center of mass of a head of a person wearing the helmet B100. A non-zero displacement between the normal component and a center of mass B90 of an assembly of the helmet B100 and the head of a person wearing the helmet B100 thereby represents a first lever arm vector Li, with the product of the normal component and the first lever arm causing a non-zero negative torque B2 of the head and helmet B100. In the absence of other forces, a negative rotation of the head with a negative direction of rotation would be induced.
Due to friction and other resistive forces, such as a rolling resistance and the like between the object and an outer layer of the helmet B100, an outer surface of the helmet B100 is

40 subject to a tangential friction force, FT, as indicated in Fig. 17. A
displacement between the center of mass B90 and the tangential friction force represents a second lever arm vector L2 with the product of the tangential friction force and the second lever arm vector corresponding to a positive torque B1 to the head and helmet B100. The positive torque B1 is directed opposite of the negative torque B2 caused by the normal component and the first lever arm vector.
Next to the sufficiently low friction between the outer surface of the helmet B100 and the head of the user required to result in negative rotation, there is a second requirement needed to observe negative rotation of the head and helmet B100 upon impact: The center of mass B90 needs to be above the normal component of the impact force in case of a vertically downwards impact (as the one indicated in Fig. 17), since a center of mass B90 below the normal component of the impact force otherwise results in an additional contribution to the positive torque, reinforcing the positive rotation. The opposite holds in an impact along a vertically upward direction (as it may occur when the person wearing the helmet collides with an obstacle like a bridge or other objects), the center of mass B90 needs to be below the normal component of the impact force (not shown in Fig. 17). However, this second requirement is generally met due to the weight of the body of the person wearing the helmet, moving the center of mass B90 away from the helmet towards the body.
Ideally, the positive and negative torques Bl, B2 cancel out, such that zero rotation occurs to head and neck and the entire head and helmet B100 slides downwards the oblique plane as a whole, as sketched in the scenario of Fig. 18a.
Depending on the magnitude of the positive and negative torques B1, B2, upon impact, the head and helmet B100 will rotate either positively (along the direction of the positive torque B1 due to the friction force, scenario shown in Fig. 18c) or negatively (along the direction of the negative torque B2 due to the normal component, opposite to the direction of the friction force, scenario shown in Fig. 18b).
In both cases, the net rotation of the head upon impact is known to cause severe injuries for the brain and neck of the person.
Now referring to Fig. 19a, a helmet B100 according to the invention comprises an inner layer B11, at least one outer protective layer B12 and a motion inhibiting layer B13, wherein upon an impact on the at least one outer protective layer B12, the at least one outer protective layer B12 is configured to move relative to the inner layer B11 and wherein the motion inhibiting layer B13 is configured to reduce a negative rotation of the helmet B100 resulting upon the impact.

41 Preferably, said inner layer B11 may comprise energy absorbing elements and/or an energy absorbing material, so as to form an energy absorbing layer.
As mentioned above, the regime of negative rotation of the helmet 3100 requires a sufficiently low friction between the various layers, particularly a sufficiently low friction transmission from the at least one outer protective layer B12 to the inner layer B11. To this end, the helmet 9100 may additionally comprise an intermediate layer 914 configured to lower the friction between the at least one outer protective layer 812 and the inner layer B11.
For example, as shown in Fig. 19a, the intermediate layer B14 may comprise rollable elements B20 that contribute to a substantially lower friction and/or rolling resistance by promoting the motion between the at least one outer protective layer B12 and the inner layer B11 upon impact.
Said rollable elements B20 may be for example rolls, beads and the like, particularly with a circular diameter between 0.1 mm and 4 mm, particularly between 1 mm and 2 mm, wherein the circular diameter refers to a circular cross-section of the rollable elements B20.
According to the invention, the inhibiting layer is configured to reduce a negative rotation of the helmet B100 resulting upon the impact. To this end, the inhibiting layer may comprise inhibiting elements, that in turn increase the friction between the at least one outer protective layer B12 and the inner layer B11, particularly in combination with the rollable elements 820 shown in Fig. 19a. The resulting net friction between the at least one outer protective layer B12 and the inner layer B11 is preferably chosen such that the rotation, particularly the negative rotation of the helmet B100 upon impact is reduced.
According to an embodiment of the present invention, at least one of the following may comprise a plurality of stacked sub-layers: the inner layer B11, the at least one outer protective layer B12, the motion inhibiting layer B13, the intermediate layer B14. The aforementioned layers may alternatively or additionally also comprise multiple mutually connected shell segments that are arranged essentially in a respective plane extending along the respective layer.
As shown in the embodiment illustrated in Fig. 19a, the motion inhibiting layer 13 or the motion inhibiting elements B70 may be at least partially arranged within the intermediate layer B14 arranged between the at least one outer protective layer B12 and the inner layer 811, which advantageously contributes to finetune an interaction of the friction reducing intermediate layer B14 and the friction increasing motion inhibiting layer B13, so as to minimize the rotation, particularly the negative rotation of the helmet 3100 upon impact.

42 Still referring to Fig. 19a, together with the inner layer B11 and the at least one outer protective layer B12, the motion inhibiting layer B13 may delimit at least one volume B50, so as to confine at least a fraction of the rollable elements B20 in the at least one volume B50.
In this embodiment, also several volumes B50, particularly with a different number and/or different geometries of rollable elements B20 may be used to finetune the resulting net friction between the various layers, particularly between the inner layer B11 and the at least one outer protection layer upon impact.
In another embodiment of the sixth aspect of the present invention, the rollable elements B20, the inner layer B11, the intermediate layer B14, the at least one outer protective layer B12 and the motion inhibiting layer B13 comprise a lower or a larger elasticity, wherein the elasticity of the rollable elements B20 is lower or larger than the elasticity of at least one of the following: the inner layer B11, the intermediate layer B14, the at least one outer protective layer B12, the motion inhibiting layer B13. By finetuning the various elasticities, a desired net friction between the inner layer B11 and the at least one outer protective layer B12 can be achieved, so as to control the rotation, particularly the negative rotation of the helmet B100 upon impact.
For example, the lower elasticity may correspond to a young's modulus of less than 3 GPa.
For example, a rolling resistance coefficient between the intermediate layer B14 and the at least one outer protective layer B12 and/or the inner layer B11 may be below 0.2.
For example, a coefficient of friction between the intermediate layer B14 or the motion inhibiting layer B13 and the at least one outer protective layer B12 or the inner layer B11 may be below 0.8.
Fig. 19b shows various motion inhibiting elements B70. For example, the motion inhibiting elements B70 may comprise a cylinder, a cone, a pyramid, a cuboid, a truncated cone.
The motion inhibiting elements B70 are preferably configured to inhibit the relative motion between the inner layer B11 and the at least one outer protective layer B12.
The motion inhibiting elements B70 may advantageously be used in combination with the intermediate layer B14, particularly with the intermediate layer B14 comprising rollable elements B20, so as to achieve a minimum net rotation of the helmet B100 upon impact, particularly a minimum negative rotation. The particular choice of geometry for the motion inhibiting layer B13 thereby represents a tool to control the amount of friction or rolling resistance of between the intermediate layer B14 and the at least one outer layer or the inner layer B11.

43 Fig. 20 presents another embodiment of the sixth aspect of the present invention, wherein the motion inhibiting layer B13 is integrally formed with the at least one outer protective layer B12. To this end, the two integrally connected layers may form an outer shell of the helmet B100, representing the at least one outer protective layer B12, while additionally comprising motion inhibiting elements B70 that inhibit the motion of the intermediate layer B14 arranged between the outer shell and the inner layer B11. As shown in Fig. 20, the intermediate layer B14 preferably comprises the rollable elements B20. Forming the motion inhibiting layer B13 integrally with the inner layer B11 and/or the at least one outer protective layer B12 advantageously contributes to reduce fabrication costs and -time of the helmet B100.
However, this embodiment is not limited to an integral connection of only the motion inhibiting layer B13 and the at least one outer protective layer B12, but refers to any form of integral connection between at least two of the following: the at least one outer protective layer B12, the motion inhibiting layer B13, the intermediate layer B14, the inner layer B11.
Fig. 21 shows another embodiment of the sixth aspect of the present invention, in which the motion inhibiting layer B13 comprises viscous a fluid or gel B60. The viscous fluid or gel B60 may preferably be configured to introduce a shear stress to the various layers mentioned above, particularly a shear stress between the inner layer B11 and the at least one outer protective layer B12. As shown in Fig. 21, the viscous fluid or gel B60 may preferably be used in combination with rollable elements B20, wherein the viscous fluid or gel B60 may be chosen such that the interplay of the viscosity creating additional shear stress and the intermediate layer B14 reducing the friction results in a minimum net rotation of the helmet B100 upon impact, particularly a minimum negative rotation. Preferably, the viscous fluid or gel B60 may be arranged in a leak tight volume enclosed by at least the inner layer B11 and the outer protective layer B12 so as to retain the viscous fluid or gel B60.
For example, the viscous fluid or gel B60 may comprise a viscosity within 0.001 and 10 Pa s.
According to another embodiment of the sixth aspect of the invention, the motion inhibiting layer B13 may comprise a non-Newtonian fluid or gel B61. As such, the viscosity of the fluid or gel B60, B61 may depend on the shear stress, which may advantageously be used as another parameter to finetune the interplay of the fluid or gel B60, B61 creating additional shear stress and the intermediate layer B14 reducing the friction, so as to achieve a minimum net rotation of the helmet B100 upon impact, particularly a minimum negative rotation.
Fig. 22 shows another embodiment of the sixth aspect of the present invention, wherein the motion inhibiting layer B13 comprises a flexible layer B15, particularly a fabric or a webbing.

44 The intermediate layer B14, particularly the rollable elements B20, may for example be embedded in the flexible layer B15. Upon impact, resulting compression- or shearing forces caused within the flexible layer B15 may be used to counteract the relative motion between the inner layer B11 and the at least one outer protective layer B12 and particularly the negative rotation of the helmet B100. In this way, the low friction or rolling resistance provided by the rollable elements B20 may be partially compensated by the flexible layer B15, so as to fine tune the resulting net friction between the inner layer B11 and the at least one outer protective layer B12.
However, this embodiment is not limited to a flexible layer B15 arranged only between the motion inhibiting layer B13 and the intermediate layer B14, but refers to a flexible arranged between any of at least two of the following: the at least one outer protective layer B12, the motion inhibiting layer B13, the intermediate layer B14, the inner layer B11.
Fig. 23 shows another embodiment of the sixth aspect of the present invention, wherein the motion inhibiting comprises connectors B80 arranged between the at least one outer protective layer B12 and the inner layer B11.
Preferably, said connector B80 or connectors B80 may be configured to deform and/or to rupture simultaneously and/or sequentially upon the impact, so as to counteract the negative rotation of the helmet B100.
The connectors B80 may preferably be used in combination with the intermediate layer B14, particularly the intermediate layer B14 comprising rollable elements B20, wherein the choice of connectors B80 introducing friction and the intermediate layer B14 reducing friction may be adapted to achieve a minimum net rotation of the helmet B100 upon impact, particularly a minimum negative rotation.
To this end, individual connectors B80 forming the plurality of connectors B80 may comprise individual rupture forces, wherein the individual rupture forces take on at least two values. As such, a plurality of individual connectors B80 with tailored deformation or rupturing properties may be used within the motion inhibiting layer B13 to achieve a minimum net rotation of the helmet B100 upon impact, particularly a minimum negative rotation.
For example, the connectors B80 may comprise or be an adhesive, a thermoplastic, an elastonner, a ceramic or a metal.
However, this embodiment is not limited to connectors B80 arranged only arranged between the at least one outer protective layer B12 and the inner layer B11, but refers to connectors

45 B80 arranged between any of at least two of the following: the at least one outer protective layer B12, the motion inhibiting layer B13, the intermediate layer B14, the inner layer B11.

Claims

1. A helmet (1) comprising:
- A first layer (10) forming an outer surface of the helmet (1), - a second layer (30), and - a reactive layer (20) sandwiched between the first layer (10) and the second layer (30.

2. The helmet according to claim 1, wherein the reactive layer comprises a plurality of rigid balls (2) that remain rigid during normal use of the helmet (1) and are configured to roll at an impact threshold over an outer surface (30a) of the second layer (30).

3. The helmet according to claim 2, wherein the balls (2) are distributed along an inner surface (10a) of the first layer (10) such that they cover an area that corresponds to 10%
to 50%, preferably 15% to 30%, preferably about 20% of the area of said inner surface (10a) of the first layer (10).

4. The helmet according to claim 2 or 3, wherein the rigid balls (2) are bonded to a substrate film (21) via an adhesive (22) configured to undergo brittle failure.

5. The helmet according to claim 4, wherein the substrate film (21) comprises a thickness smaller than 200 pm.

6. The helmet according to claim 4 or 5, wherein the substrate film (21) comprises an adhesive layer (23) preferably consisting of a pressure sensitive adhesive arranged on a side of the substrate film (21) facing away from said plurality of balls (2).

7. The helmet according to claim 4 or according to one of the claims 5 to 6 insofar referring to claim 4, wherein the reactive layer (20) is a membrane (20) bonded to the first and the second layer (10, 30), wherein the membrane (20) comprises said substrate film (21) and the plurality of balls (2) arranged thereon.

8. The helmet according to claims 6 and 7, wherein the membrane (20) is bonded to an outer surface (30a) of the second layer (30) via said adhesive layer (23) of the substrate film (21).

9. The helmet according to one of the claims 7 to 8, wherein the membrane (20) is bonded to an inner surface (10a) of the first layer (10) via an adhesive layer (14), preferably an adhesive layer (14) comprising a thermo-softening adhesive.

4(

10. The helmet according to claim 9, wherein the first layer (10) comprises a sheet (11), a color layer (12) arranged on an inner surface of the sheet (11), a protective layer (13) arranged on the color layer (12), wherein said adhesive layer (14) that bonds the membrane (20) to the inner surface of the first layer (10) is bonded to the protective layer (13).

11. The helmet according to claim 10, wherein the protective layer (13) is a heat resistant ink layer_

12. The helmet according to claim 10, wherein the protective layer (13) is a plastic layer.

13. The helmet according to one of the claims 10 to 12, wherein the protective layer (13) comprises a thickness below 0.1 mm and/or a yield strength larger than 20 MPa.

14. The helmet according to one of the claims 10 to 13, wherein the protective layer (13) has a thermal expansion differing less than 5 % from a thermal expansion of a material of the first layer (10).

15. The helmet according to one of the claims 1 to 9, wherein the first layer (10) that is a twin sheet assembly comprising an outer sheet (11) and an inner sheet (110).

16. The helmet according to claim 15, wherein the inner sheet (110) of the twin sheet assembly (10) is perforated.

17. The helmet according to claim 15 or 16, wherein a color layer (12) and an adhesive layer (140) are arranged between the outer and the inner sheet (11, 110), wherein particularly the color layer (12) is arranged on the outer sheet (11) and the inner sheet (110) is bonded to the outer sheet (11) via the adhesive ink layer (140).

18. The helmet according to one of the preceding claims, wherein the helmet (1) comprises an energy absorbing layer (40), wherein an inner surface (30b) of the second layer (30) is bonded to the energy absorbing layer (40) by an adhesive layer (33).

19. The helmet according to claim 18, wherein the second layer (30) comprises recesses and/or through-holes through which portions of the energy absorbing layer (40) extends towards the first layer (10), said portions of the energy absorbing layer (40) being bonded to the first layer (10).

20. The helmet according to claim 19, wherein an outer surface of the second layer (30) locally bends upwards around the respective recess and/or through-hold to reduce a separation between an inner surface of the first layer (10) and said outer surface of the second layer (30), particularly so as to avoid a bleeding of the energy absorbing layer (40) into a volume between said inner and outer surfaces during manufacturing of the energy absorbing layer (40).

21. The helmet according to one of the preceding claims, wherein the reactive layer (20) is configured to facilitate relative movement between the first layer (10) and the second layer (30) by the rolling of balls (2) of said plurality of balls (2) between the first and the second layer (10, 30), wherein said rolling of balls (2) provides a low rolling resistance in the range from 0.0001 to 0.2, particularly 0.03 to 0.05, particularly 0.025 to 0.04, between the balls (2) and an inner surface (10a) of the first layer (10) or connected to the first layer (10) or between the balls (2) and an outer surface (30a) of the second layer (30) or connected to the second layer (30).

22. The helmet according to one of the preceding claims, wherein the inner surface (10a) of the first layer (10) and the outer surface (30a) of the second layer (30) are concentric with respect to one another.

23. The helmet according to one of the preceding claims, wherein the membrane (20) or reactive layer (20) is congruent to an inner surface of the first layer (10).

24. The helmet according to one of the preceding claims, wherein the second layer (30) forms at least one ramp to cause the first layer (10) to bend away from the second layer (30) to avoid butting up of the first layer (10) on a portion of the second portion.

25. The helmet according to one of the preceding claims, wherein the energy absorbing layer (40) and/or the second layer (30) comprises an edge portion (80) having a chamfered or rounded edge (80a) to prevent a trailing edge (10g) of the first layer (10) from becoming caught on said edge portion (80) when moving relative to the second layer (30) and/or energy absorbing layer (40) over said edge portion (80)

26. The helmet according to one of the preceding claims, wherein the reactive layer (20) is configured to hold the first layer (10) such that a tangential force required to activate rolling of balls (2) of the reactive layer is about 0.1kN, or such that an energy introduced by the impact force (FT) has to exceed 2.5J to activate rolling of the balls (2).

27. The helmet according to one of the preceding claims, wherein an outer surface (30a) of the second layer (30) comprises a plurality of protrusions that provide resistance to the rolling of balls (2) of said plurality of balls (2).

28. The helmet according to one of the preceding claims, wherein the first layer (10) comprises a front portion (101) connected to the energy absorbing layer (40) causing the front portion (101) of the first layer (10) to remain in place during an oblique impact in a first direction (D1) from a rear of the helmet (1) towards the front of the helmet (1), while a remaining portion (102) of the first layer (10) being connected to the front portion (101) is separated from the second layer (30), and wherein, during an oblique impact in a second direction (D2) from the front of the helmet (1) towards the rear from the helmet (1), the front portion (101) is configured to disengage from the energy absorbing layer (40) or the remaining portion of the first layer (10) is configured to tear apart from the front portion of the first layer (10).

29. The helmet according to claim 28, wherein said front portion (101) forms a tab comprising an opening (103), the tab being embedded in the energy absorbing layer (40), wherein a portion (400) of the energy absorbing layer (40) extends through said opening (103) such that said portion (400) holds the tab in place upon said oblique impact in the first direction (D1) and preferably breaks to release the tab upon said oblique impact in the second direction (D2).

30. The helmet according to one of the preceding claims, wherein upon an impact force on the first layer (10), the first layer (10) is configured to deform in shape and move relative to the second layer (30).

31. The helmet according to one of the preceding claims, wherein the first layer (10) comprises an edge region (10b), wherein the edge region (10b) is configured to inhibit a transfer of a radial force (FR) from the first layer (10) to the second layer (30).

32. The helmet according to claim 31, wherein said edge region (10b) is formed by a portion of the first layer (10) extending at an angle (x) with respect to a normal of an outer surface of the second layer (30), said angle (x) being in the range from 20 to 800, preferably 30 to 70 , preferably 40' to 60', preferably 40 to 50 .

33. The helmet according to one of the claims 1 to 30, wherein the first layer (10) comprises an edge region (10b) that is connected to an outer surface (30a) of the second layer (30) by a compressible intermediary layer (4), particularly to inhibit a transfer of a radial force (FR) from the first layer (10) to the second stiff layer

34. The helmet according to one of the preceding claims, wherein the first layer (10) is configured to store and release energy as a result of an impact to the first layer (10) to reduce rotational motion of a head of a person wearing the helmet (1).

35. The helmet according to one of the preceding claims, wherein the first layer (10) is configured to change its shape relative to the second layer (30) during irnpact, wherein particularly the first layer (10) comprises an auxetic structure.

36. The helmet according to one of the preceding claims, wherein the first layer (10) is shaped to pivot the helmet (1) during impact and thereby reduce rotational motion of a head of a person wearing the helmet (1).

37. The helmet according to wherein the first layer (10) is configured to deform during an impact such that a free movement of the first layer (10) is inhibited during impact, wherein particularly said deformation causes a peeling of an adhesive (22) bonding the balls (2) to the outer surface (30a) of the second layer (30).

38. The helmet according to claim 36, wherein the first layer (10) comprises a buckling (5) for supporting said pivoting.

39. The helmet according to claim 2 and according to claim 37, wherein upon an impact, the buckling (5) is configured to flatten and increase in width resulting in a translational movement of a boundary region (50) of the buckling causing the balls (2) to roll.

40. The helmet according to claim 38, wherein the buckling (5) is configured to provide a redirection of a normal force of an impact acting on the first layer (10) such that the normal force comprises a distance (A) to the center of mass (C) of the system comprised of the helmet (1) and a head of a person wearing the helmet (1).

41. The helmet according to one of the preceding claims, wherein the first layer (10), particularly the buckling (5), is configured to deform on impact to prevent geometric locking of the first layer (10) due to a mechanical interaction with an adjacent structure of the helmet (1), wherein particularly deformation of the first layer (10), particularly of the buckling (5), causes an edge region (51) of the first layer (10) to lift up from the reactive layer (20) so as to not become entangled with adjacent structures of the helmet (1).

42. The helmet according to one of the preceding claims, wherein an inner surface (10a) of the first layer (10) is configured to become congruent with an outer surface (30a) of the second layer (30) during an impact, particularly so as to increase the duration of impact and sliding before contact.

43. The helmet according to one of the preceding claims, wherein the first layer (10) contacts the reactive layer (20) merely via one or several restricted portions of an inner surface (10a) of the first layer (10), wherein particularly said portion(s) is/are arranged at a perimeter of the first layer (10).

44. The helmet according to claim 43, wherein said portion(s) comprise an increased stiffness compared to an adjacent portion of the first layer (10), particularly so as to reduce the area of the reactive layer necessary for facilitating relative movement between the first layer (10) and the second layer (30).

45. The helmet according to one of the preceding claims, wherein the first layer (10) is an injection-moulded first layer (10) and/or wherein the second layer (30) is an injection-moulded second layer (30).

46. The helmet according to one of the preceding claims, wherein a portion of an inner surface of the first layer (10) is bonded to a portion of an outer surface of the second layer (30).

47. The helmet according to one of the preceding claims, wherein the first layer (10) is connected to the second layer (30) by connectors (6), the respective connector (6) protruding from an inner surface (10a) of the first layer (10) and extending through an associated through-opening (300) of the second layer (30) with an end portion (60) of the connector (6), the end portion (60) engaging with the second layer (30) to connect the first layer (10) to the second layer (30), wherein the respective connector (6) is configured to break at said impact threshold to release the first layer (10) from the second layer (30).

48. The helmet according to one of the preceding claims, wherein the first layer is a sacrificial layer configured to smooth out a surface impacting on the helmet to allow the balls to roll on it, wherein the sacrificial layer is configured to be completely or partially released from the helmet during an oblique impact and particularly configured to not translate during said impact relative to the impacting surface.

49. The helmet according to one of the preceding claims, wherein an energy necessary to release each ball is in the range between 0.005 Joules and 0.5 Joule per ball.

50. The helmet comprises a plurality of first layers (10), and a reactive layer (20) sandwiched between each first layer (10) and the second layer (30).

51. A method for manufacturing a helmet, particularly a helmet (1) for cycling, particularly a helmet (1) according to one of the preceding clairns, wherein the method comprises the steps of:
(a) Providing a first layer (10) and an adhesive layer (14) arranged thereon, (b) Providing a second layer (30) and an adhesive layer (33) arranged thereon, (c) Providing a membrane (20) comprising a plurality of balls bonded to a substrate film (21) of the membrane (20) using an adhesive (22), the substrate film (21) comprising an adhesive layer (23) on a side facing away from said plurality to balls, (d) Arranging the membrane (20) on an outer side (30a) of the second layer (30) and bonding the membrane (20) to the second layer (30) via said adhesive layer (23) of the substrate film (21), (e) Arranging the first layer (10), the second layer (30) and the membrane (20) in a cavity of a mould, wherein the membrane (20) is arranged between the first and the second layer (10, 30), and (f) Providing a material in the cavity adjacent the adhesive layer (33) arranged on the second layer (30) for forming an energy absorbing layer (40) of the helmet (1), wherein the energy absorbing layer (40) is bonded to an inner surface (30b) of the second layer (30) via said adhesive layer (33) arranged on the second layer (30), and bonding the plurality of balls (2) to the first layer (10) via said adhesive layer (14) arranged on the first layer (10).

52. The method according to claim 51, wherein the adhesive layer (14) arranged on the first layer (10) is a thermo-softening adhesive layer (14), and/or wherein the adhesive layer (33) arranged on the second layer (30) is a thermo-softening adhesive layer (33), and/or wherein the adhesive layer (23) of the substrate film comprise a pressure sensitive adhesive.

53. The method according to claim 51 or 52, wherein providing a first layer (10) in step (a) comprises proving a sheet (11), applying a color layer (12) on the sheet (11), wherein thereafter preferably a light bleed preventing base coat is applied on the color layer 12, applying a protective layer (13) on the color layer (12), and wherein arranging said adhesive layer (14) on the first layer (10) comprises arranging said adhesive layer (14) on the protective layer (13).

54. The method according to one of the claims 51 to 53, wherein providing the second layer (30) in step (b) comprises proving a sheet (31), applying a color layer (32) on the sheet (31) of the second layer (30), wherein thereafter preferably a light bleed preventing base coat is applied on the color layer 32, and wherein arranging said adhesive layer (33) on the second layer (30) comprises arranging said adhesive layer (33) on the color layer (32) of the second layer (30).

55. The method according to one of the claims 51 to 54, wherein the step (c) of providing the membrane (20) cornprises providing the substrate film (21) by kiss cutting a laminate (7) comprising a top layer (70) and a backing (71), the substrate film (21) being kiss cut from the top layer (70) resulting in the substrate film (21) arranged on the backing (71) and in a surrounding portion (72) of the top layer (70), wherein particularly the substrate film (21) comprises an elongated shape being adapted to a geometry of a corresponding portion of the outer surface (30a) of the second layer (30).

56. The method according to claim 55, wherein step (c) further comprises:
- removing said surrounding portion (72), - arranging dots of said adhesive (22) onto the substrate film (21), and - placing a ball (2) of said plurality of balls on each dot of adhesive (22) to bond the balls (2) to the substrate film (21).

57. The method according to claim 55, wherein step (c) further comprises:
- applying a layer of said adhesive (22) onto the substrate film (21), - removing said surrounding portion (72), and -placing said plurality of balls (2) on the layer of said adhesive (22) to bond the balls (2) to the substrate film (21).

58. The rnethod according to one of the claims 51 to 57, wherein the second layer (30) comprises recesses and/or through-holes through which the material is made to extend towards the first layer (10) to bond with the first layer (10).

59. A helmet (B100) for protecting the head of a person upon an impact, the helmet (B100) comprising an outer surface, the helmet (9100) being configured to reduce negative rotation of a head of the person wearing the helmet (B100) resulting from an impact force acting on the outer surface of the helmet (B100) upon said impact.

60. The helmet (B100) according to claim 59, wherein said negative rotation results from a negative torque (B2) corresponding to the cross product of the normal component (FN) of the impact force, which normal component extends perpendicular to the outer surface, and a first lever arm vector (Li) between the center of mass (B90) of an assembly formed by said head and helmet (B100) and the normal component (FN).

61. The helmet (B100) according to claim 59 or 60, wherein for reducing said negative rotation the helmet (B100) comprises at least one motion inhibiting element (B70).

62. The helmet (B100) according to one of the claims 59 to 61, wherein the helmet (B100) comprises at least one outer protective layer (B12) forming said outer surface and an inner layer (B11), wherein for reducing a positive rotation of the head of the person upon said impact, the at least one outer protective layer (B12) is configured to move relative to the inner layer (911).

63. The helmet (B100) according to claim 62, wherein said positive rotation is opposite the negative rotation and results from a positive torque (B1) corresponding to the cross product of a tangential friction force (FT) acting on the outer surface of the helmet (B100) upon said impact and a second lever arm vector (L2) extending parallel to said normal component (FN) to the center of mass (B90).

64. The helmet (B100) according to one of the claims 60 to 63, wherein the at least one motion inhibiting element (B70) is adapted such that the negative torque (B2) counteracts the positivetorque (B1) leading to an angular rotation velocity of the helmet (B100) and head upon said impact in the range from -15 rad/s to +15 rad/s, preferably -10 rad/s to +10 rad/s, more preferably -5 rad/s to +5 rad/s.

65. The helmet (B100) according to one of the claims 59 to 64, wherein the at least one motion inhibiting element (B70) is arranged between the inner layer (B11) and the at least one outer protective layer (B12).

66. The helmet (B100) according to one of the claims 61 to 65, wherein the motion inhibiting element (B70) comprises or is a motion inhibiting layer (913).

67. The helmet (B100) according to claim 66, wherein the motion inhibiting layer (B13) is integrally formed with the inner layer (B11) and/or the at least one outer protective layer (B12).

68. The helmet (B100) according to claim 66 or 67, wherein the motion inhibiting layer (B13) is configured to deform upon the impact force.

69. The helmet (B100) according to one of the claims 62 to 6, further comprising an intermediate layer (B14) arranged between the inner layer (B11) and the at least one outer protective layer (B12), said intermediate layer (B14) being configured to promote the relative motion between the inner layer (B11) and the at least one outer protective layer (B12).

70. The helmet (B100) according to one of the claims 66 to 69, wherein the motion inhibiting layer (B13) comprises a flexible layer (B15), particularly a fabric or a webbing arranged between the motion inhibiting layer (913) and at least one of the following:
the inner layer (B11), the intermediate layer (B14), the at least one outer protective layer (B12).

71. The helmet (B100) according to claim 70, wherein the flexible layer (B15) is configured to counteract the motion of the intermediate layer (B14) upon the impact.

72. The helmet (B100) according to one of the claims 62 to 71, wherein at least one of the following comprises a plurality of stacked sub-layers: the inner layer (B11), the at least one outer protective layer (B12), the motion inhibiting layer (B13), the intermediate layer (B14).

73. The helmet (B100) according to one of the claims 66 to 72, wherein the motion inhibiting layer (B13) is arranged at least partially within the intermediate layer (B14).

74. The helmet (B100) according to one of the claims 69 to 73, wherein the intermediate layer (B14) is integrally formed with at least one of the following: the inner layer (B11), the motion inhibiting layer (B13), the at least one outer protective layer (B12).

75. The helmet (B100) according to one of the claims 69 to 74, wherein the intermediate layer (B14) and/or the motion inhibiting layer (B13) comprises rollable elements (B20), said rollable elements (B20) being configured to promote the motion of the inner layer (B11) relative to the at least one outer protecting layer (B12) upon the impact.

76. The helmet (B100) according to claim 75, wherein the intermediate layer (B14) and/or the motion inhibiting layer (B13) cornprises breaking elements configured to fail upon the impact, enabling the rollable elements (B20) to interact with the inner layer (B11) and the at least one outer protective layer (B12), so as to promote the motion of the inner layer (B11) relative to the at least one outer protecting layer (B12).

77. The helmet (B100) according to claim 75 or 76, wherein together with the inner layer (B11) and the at least one outer protective layer (B12), the motion inhibiting layer (B13) defines at least one volume (B50), so as to confine at least a fraction of the rollable elements (B20) in the at least one volume (B50).

78. The helmet (B100) according to one of the claims 75 to 77, wherein an elasticity of the rollable elements (B20) is lower or larger than an elasticity of at least one of the following:
the inner layer (B11), the intermediate layer (B14), the at least one outer protective layer (B12), the motion inhibiting layer (B13).

79. The helmet (B100) according to claim 78, wherein the lower elasticity corresponds to a young's modulus of less than 3 GPa.

80. The helmet (B100) according to one of the claims 69 to 79, wherein a rolling resistance coefficient between the intermediate layer (B14) and the at least one outer protective layer (B12) and/or the inner layer (B11) is below 0.2.

81. The helmet (B100) according to one of the claims 66 to 80, wherein a coefficient of friction between the motion inhibiting layer (B13) and the intermediate layer (B14) or the at least one outer protective layer (B12) or the inner layer (B11) differs from a coefficient of friction between the intermediate layer (B14) and the at least one outer protective layer (B12) or the inner layer (B11).

82. The helmet (B100) according to one of the claims 66 to 81, wherein a coefficient of friction between the intermediate layer (B14) or the motion inhibiting layer (B13) and the at least one outer protective layer (B12) or the inner layer (B11) is below 0.8.

83. The helmet (B100) according to one of the claims 66 to 82, wherein the motion inhibiting layer (B13) comprises a viscous fluid or gel (B60).

84. The helmet (B100) according to claim 83, wherein the viscous fluid or gel (B60) comprises a viscosity within 0.001 Pa s and 10 Pa s.

85. The helmet (B100) according to one of the claims 66 to 82, wherein the motion inhibiting layer comprises a non-Newtonian fluid or gel (B61).

86. The helmet (B100) according to one of the claims 59 to 85, wherein individual motion inhibiting elements (B70) forming the motion inhibiting elements (B70) are configured to rupture upon a predetermined rupture force caused by the impact, and wherein a geometrical feature, particularly a diameter, a width or a length of an individual inhibiting element (B70) is indicative for an individual rupture force required to rupture an individual inhibiting element (B70), said rupture force counteracting the negative rotation of the helmet (B100) upon the impact.

87. The helmet (B100) according to one of the claims 62 to 86, wherein the motion inhibiting elements (B70) cover less than 80% of a total lateral surface area defined by the at least one outer protective layer (B12).

88. The helmet (B100) according to one of the claims 59 to 87, wherein the motion inhibiting elements (B70) are formed as at least one of the following: a cylinder, a cone, a pyramid, a cuboid, a truncated cone.

89. The helmet (B100) according to one of the claims 62 to 88, wherein the motion inhibiting elements (B70) contact the at least one outer protective layer (B12) and the inner layer (B11) via a lateral contact surface area, wherein a ratio of the lateral contact surface area and the total lateral surface area is within 0.05 and 0.5.

90. The helmet (B100) according to one of the claims 66 to 89, wherein the motion inhibiting layer (B13) comprises a connector (B80) being integrally formed with at least two of the following: the inner layer (B11), the intermediate layer (B14), the at least one outer protective layer (B12).

91. The helmet (B100) according to claim 90, said connector (B80) being configured to deform and/or to rupture upon the impact.

92. The helmet according to claim 91, wherein the rnotion inhibiting layer (B13) comprises a plurality of connectors (B80), said connectors (B80) being configured to deform and/or rupture simultaneously and/or sequentially upon the impact.

93. The helmet (B100) according to claim 92, wherein individual connectors (B80) forrning the plurality of connectors (B80) comprise individual rupture forces, said individual rupture forces taking on at least two values and wherein the rupture forces counteract the negative rotation of the helmet (B100) upon the impact.

94. The helmet (B100) according to one of the claims 90 to 93, wherein the connector (B80) comprises or is an adhesive.

95. The helmet (B100) according to one of the claims 90 to 94, wherein the connector (B80) has a different elasticity or stiffness than the inner layer (B11) and/or the at least one outer protective layer (B12).

96. The helmet (B100) according to one of the claims 90 to 95, wherein the connector (B80) comprises at least one of the following: a thermoplastic, an elastomer, a ceramic or a metal.

97. The helmet (B100) according to one of the claims 59 to 96, wherein the motion inhibiting layer (B13) comprises at least one of the following: a plastic material, an elastic material, a polymer, a metal.

98. The helmet (B100) according to one of the claims 66 to 97, wherein the motion inhibiting layer (B13) is configured such that the reduction of negative rotation of the helmet (B100) depends on a direction of the impact, particularly a direction of the tangential friction force (FT).

99. The helmet (B100) according to claim 98, wherein the motion inhibiting layer (B13) is configured such that the reduction of negative rotation upon an impact resulting in a rotation of the helmet (B100) around a first axis is larger than the reduction of negative rotation upon an impact resulting in a rotation of the helmet (B100) around a second axis.

100. The helmet (B100) according to claim 99, wherein the first axis extends through a coronal plane within a head of a person wearing the helmet (B100) and wherein the second axis extends through a sagittal plane within the head of the person wearing the helmet (B100).

101. The helmet (B100) according to one of the claims 62 to 100, wherein at least two of the following are configured to geometrically and/or mechanically lock so as to reduce the negative rotation upon impact: the inner layer (B11), the intermediate layer (B14), the motion inhibiting layer (B13), the outer protective layer (B12).

102. The helmet (B100) according to one of the claims 61 to 101, wherein in the absence of the motion inhibiting elements (B70) or the motion inhibiting layer (B13), upon impact, the helmet (B100) would experience negative rotation, or exceed a pre-defined positive threshold of positive rotation.

103. The helmet (1, B100) according to one of the preceding claims, wherein the rigid balls (2) are separated from one another, particularly so as to reduce contact between balls (2) upon rolling of the balls (2).

104. The helmet (1) according to one of the claims 1 to 58, wherein the rigid balls (2) are spaced apart from one another, particularly so as to reduce contact between balls (2) upon rolling of the balls (2).

105. The helmet (1) according to one of the claims 1 to 58, wherein the substrate film (21) has applied thereto an ink coloring dye and/or is stiff so as to prevent movement of the balls (2) during processing.

106. The helmet (1) according to one of the claims 1 to 58, wherein the first layer (10) is configured to flex during an impact.