EP0021842B1

EP0021842B1 - Sheet member, mattress assembly and methods of making a bed

Info

Publication number: EP0021842B1
Application number: EP19800302175
Authority: EP
Inventors: Peter Thomas Lowthian
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1979-06-28
Filing date: 1980-06-27
Publication date: 1984-02-08
Also published as: GB2055569A; GB2055569B; DE3066489D1; EP0021842A1

Description

The present invention relates to a sheet member for combination with other sheet members to cover a mattress, to a mattress assembly, and to a method of making a bed. The invention is concerned in particular but not exclusively with a sheet member, a mattress assembly and a method of using such an assembly, for use with patients in hospital beds.
In present known practice, it is found that a large proportion of hospital mattresses are still protected by a waterproof mattress cover, a bottom (cotton)sheet, a draw-mackintosh (usually a plastic sheet) and a cotton twill drawsheet as the uppermost layer. The waterproof draw-mackintosh (referred to as a draw-mack) and the upper cotton sheet (referred to as the drawsheet) are ordinarily positioned over the central portion of the mattress and are tucked under the long edges of the mattress at each side.
Drawsheets and draw-macks continue to be used on new types of mattresses and special support systems, despite manufacturers' recommendations against using them. This practice has been particularly noticeable on ripple mattresses and on water beds. It seems clear that the drawsheet/draw-mack/bottom sheet system is undesirable from the patient comfort aspect, but the system has persisted for a number of reasons which may be summarised as follows:-

(1) the system is convenient for speed of changing when used for incontinent patients;
(2) use of the method minimises the disturbance of very ill patients when their bed linen has to be changed, due to incontinence, wound discharge, bleeding, and so on;
(3) long stay bed-fast patients who take their meals in bed often stain their bottom sheet, and it is found easier if the nurses merely have a drawsheet to change rather than a full bottom sheet; and
(4) drawsheets are relatively cheap and have a long laundry life (about 200 washes).

It is one object of the present invention, at least in preferred embodiments thereof, to provide a system of mattress covering which will maintain substantially all of the features of the current drawsheet/draw-mack/bottom sheet system set out above, but with improved standards of comfort for the patient.
The present invention is concerned with problems in two main areas, namely comfort of a patient in a hospital bed, and economy in use of bed linen in hospitals where sheets are frequently soiled. One attempted solution is described in US patent specification No. 3,394,416 (Hale), where a mattress assembly is shown with three sheet members positioned transversely across a bed so that a central sheet member, positioned between a head sheet member and a foot sheet member, can be changed when soiled without changing the head and toot sheet members. However, this system suffers from disadvantages of patient discomfort (the junctions of the sheet members give rise to unevenness and tucking), and lack of economy (due to complicated construction of sheet members, and inability to use the sheet members interchangeably).
In accordance with the present invention there is provided a sheet member for combination with two other sheet members to form a sheet assembly for a mattress, said sheet member having dimensions adapted for the sheet member to be positioned transversely across a single bed mattress of conventional shape and size to provide a covering for part of the length of the mattress, said sheet member being formed by a member which is a substantially flat planar member when not in use on a mattress, said sheet member comprising a main portion adapted to provide a contact surface for a user of a mattress on which the sheet member is used, characterised in that said sheet member comprises an underlie portion of smaller area than said main portion and adapted for underlying part of another sheet member when in use on a mattress, said underlie portion having a thickness less than the thickness of said main portion, and side flaps extending laterally from the sides of said sheet member at or in the region of the said underlie portion for retaining said sheet member in position on a mattress.
In one preferred form, said sheet member has on each side thereof a side flap which, when laid coplanar with the remainder of said sheet member, has at least a portion which extends laterally at an angle of inclination to the side of said sheet member.
Preferably a portion of such a flap extends in use along the direction of the length of the bed beyond an end of the sheet member at which the said underlie portion is situated.
Also in a preferred form, said main portion of said sheet member comprises an upper covering layer providing said contact surface, a layer of synthetic plastics foam or other washable cushioning material, and a bottom layer of backing material.
Most preferably at least the upper covering layer of the said main portion is formed of smooth but absorbent material (such as towelling material) which is attached by quilting stitch, or bonded, to the foam layer which may also in turn be bonded to the backing material.
Alternatively, in place of the composite structure described, the sheet member may be formed by a natural or synthetic fleece, the said underlie portion being produced for example by shaving off or otherwise removing the upper part of the fleece to leave the backing part of the fleece.
Preferably the said side flaps are made of high-friction material and may also be made of the same material as the underlie portion.
In accordance with the invention, three sheet members may be combined together to form a mattress assembly.
Thus there is also provided in accordance with the invention a mattress assembly comprising a mattress, a first sheet member positioned transversely across the mattress at the head of the mattress, a second sheet member positioned transversely across the mattress at a position intermediate the head and the foot of the mattress, and a third sheet member positioned transversely across the mattress at the foot of the mattress, each said sheet member comprising a main portion adapted to provide a contact surface for a user of a mattress on which the sheet member is used, characterised in that said first, second and third sheet members are of substantially identical size, shape and construction, and each sheet member is formed by a member which is a substantial flat planar member when removed from said mattress, each said sheet member comprising an underlie portion of smaller area than said main portion and adapted for underlying part of another sheet member when in use on a mattress, said underlie portion having a thickness less than the thickness of said main portion, and side flaps extending laterally from the sides of said sheet member at or in the region of the said underlie portion for retaining said sheet member in position on a mattress, said first sheet member being positioned with said underlie portion thereof and part of said main portion thereof folded to leave only part of said main portion exposed on top of said mattress, said second sheet member being positioned with said underlie portion thereof underlying part of said main portion of said first sheet member, and with said main portion of said second sheet member closer to the head of the mattress than to the foot of the mattress, and said third sheet member being positioned with said underlie portion thereof underlying part of said main portion of said second sheet member.
Such an assembly is advantageous as it allows for the regions of junction between the sheet members to be positioned away from the heavy and/or protruding parts of the body of a patient using a mattress upon which the sheet members are positioned.
In one preferred form said first sheet member is positioned with said underlie portion thereof and part of said main portion thereof folded around the head of the mattress to leave only part of said main portion exposed on top of said mattress, said underlie portion of said first sheet member being positioned under said mattress, and at least part of each side flap leading upwardly from said folded part of said first sheet member and being tucked between the top of said mattress and said exposed part of said first sheet member which is on top of said mattress, said second sheet member being positioned with said side flaps of said second sheet member leading downwardly and being tucked under said mattress, and said third sheet member being positioned with said side flaps of said third sheet member leading downwardly and being tucked under said mattress.
When using sheet members according to the invention there may be provided a method of making a bed comprising the steps of positioning across a mattress three sheet members to provide a covering over the mattress for a user of the mattress to lie or sit on, characterised by the steps of positioning transversely across said mattress at the head of the mattress a first sheet member, folding said underlie portion of said first sheet member and part of said main portion of said first sheet member so as to leave only part of said main portion of said first sheet member exposed on top of said mattress, positioning. transversely across said mattress at a position intermediate the head and the foot of the mattress a second sheet member and substantially identical to the first sheet member, arranging said second sheet member with said underlie portion thereof underlying part of said main portion of said first sheet member, and with said main portion of said second sheet member closer to the head of the mattress than to the foot of the mattress, positioning transversely across said mattress at the foot of the mattress a third sheet member, and substantially identical to the first sheet member, and arranging said third sheet member with said underlie portion thereof underlying part of said main portion of said second sheet member.
Preferably the method includes the steps of tucking around the sides of said mattress said side flaps extending laterally of each said sheet member so as to retain each said sheet member on said mattress.
In one particular form, said method includes the steps of folding said underlie portion and part of said main portion of said first sheet member around the head of said mattress so as to position said underlie portion of said first sheet member under said mattress, and lifting part of each side flap of said first sheet member upwardly from said folded part of said first sheet member and tucking said part of said side flap between the top of said mattress and said exposed part of said first sheet member which is on top of said mattress.
Where reference is made to a sheet member being positioned across a mattress, it is meant that the main portion of the sheet member may extend completely across the mattress from side to side thereof, or substantially completely across the mattress, or completely across the mattress and may extend beyond the width of the mattress.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-

Figure 1 is a perspective view (not to scale) from above of a sheet member embodying the invention for use in covering a mattress;
Figure 1 (a) is a perspective view (not to scale) of a modification of part of the sheet member shown in Figure 1;
Figures 2 and 3 are side and plan views of a mattress assembly embodying the invention in which three sheet members as shown in Figure 1 are positioned on a mattress;
Figure 4 is a perspective view (not to scale) from above of the mattress assembly shown in Figures 2 and 3, but with one sheet member partially removed;
Figure 5 is a perspective view (not to scale) from above of a second embodiment of a sheet member embodying the invention;
Figures 6 and 7 are side and plan views respectively of a second embodiment of a mattress assembly in which three sheet members as shown in Figure 5 are positioned on a mattress.

Referring firstly to Figures 1 to 4, there will be described a sheet assembly suitable for the majority of adult hospital beds, including contouring beds, water beds and so-called "Net" suspension beds. In most cases the assembly is also usable on domestic (single) beds, so-called ripple mattresses and ventilated mattresses. However, with reference to the drawings, the assembly will be described in use on a conventional single-size adult hospital mattress.
In Figure 1 there is shown in perspective view a single sheet member 11 comprising a main portion 12 and an underlie portion 13 from which extend two side flaps 14 and 14'. In Figure 1 (which is not to scale) the flaps 14 and 14' are shown extended in the same plane as the plane of the main portion 12 and underlie portion 13. The main portion 12 is formed of upper and lower layers 16 and 16' of stretch towelling secured by a continuous quilting stitch along lines 40 to an inner layer 17 of polyether foam. The underlie portion 13 is conveniently made of conventional cotton sheeting, and is of lesser thickness than the thickness of the main portion 12. The flaps 14 and 14' are made of high friction material for tucking under the mattress to secure the sheet member 11.
Referring to Figures 2, 3 and 4 in addition to Figure 1, a mattress 19 is covered by three sheet members 11, 22 and 23, of which the sheet member 11 has been shown in Figure 1. The sheet members 22 and 23 are of identical construction to the sheet member 11. The sheet member 22 is positioned at the head of the bed (relative to the intended position of the occupant of the bed) and the sheet member 23 is positioned at the foot of the bed.
The three sheet members 11, 22 and 23 are positioned across the mattress adjacent to one another with an underlie portion 26 of sheet member 23 underlying part of the sheet member 11, and the underlie portion 13 of the sheet member 11 underlying part of the sheet member 22. As shown in Figures 2 and 3, the side flap 14 of the sheet member 11 is tucked under the mattress 19, as is the side flap 14' (not shown). The side flaps of the sheet member 23 (of which one is indicated at 24) are tucked in similar fashion under the mattress 19.
The folding of the head sheet member 22 is arranged differently from the sheet members 11 and 23. One side flap of the sheet member 22 is indicated at 25 (the other not being visible in the drawings) and the underlie portion of the sheet member 22 is indicated at 27. For the end sheet member 22, the underlie portion 27 is not arranged to underlie another sheet member, but instead is tucked under the mattress 19 along the short, head side of the mattress. As is shown in Figures 2 and 3, the side-flap 25 extending from the underlie portion 27 of the head end sheet is then folded back upwardly along the long side of the mattress 19 and is tucked under the main portion of the sheet member 22 (the main portion being indicated at 28). As shown particularly in Figure 1, there may be provided an indelible line 41 marked on each of the flaps 14, 14' and so on, to assist in the folding of the flaps. This line 41 is used to position the head sheet member 22 to allow easy folding of the flap 25 under the main portion 28.
Figure 4 shows the mattress assembly with one sheet member 11 pulled slightly to one side, to illustrate for purposes of explanation the interrelationships between the various sheet elements.
As has been mentioned, the main portion of the sheet member 11 shown in Figure 1 is formed of a core 17 of synthetic plastics foam material. This gives the effect of the sheet member 11 (and also the other members 22 and 23) forming a pad, and in the next following description, the sheet members will be referred to as pads.
In use the three pads 11, 22 and 23 are laid directly onto the waterproof cover of the mattress 19. Preferably the mattress cover has a water vapour permeability of about 1,000 to 2,000 g/m²/day at 40°C by the so-called _'Payne's cup test method. The waterproof cover is the only waterproof part of the mattress. By way of example, the appropriate materials for such a cover are described in the UK Patent Specification No. 1341325 at line 110 on page 2 to line 35 on page 3 and in UK Patent Specification No. 1443759 at lines 6 to 22 on page 3. Conveniently the central pad 11 is changed (when soiled) as follows:-

(a) A clean pad (not shown) is obtained and rolled up by one of the two nurses performing the task. The rolling starts from one of the flap sides of the pad and the other flap is left free.
(b) The patient is rolled on his side to the edge of his mattress and cleaned (if necessary).
(c) The soiled pad 11 is rolled up under the patient (starting with the free flap 14 and including the underlie extension 13) as it is pulled from under the head pad 22.
(d) The cover surface of the mattress 19 is wiped clean (if necessary).
(e) The new pad (not shown) is placed in position, the free flap is tucked under the mattress, and the pad is unrolled until it meets the partially rolled soiled pad 11.
(f) The overlap extension of the new pad is eased under the head pad 22 as far as it will go.
(g) The patient is now rolled back to the opposite side of the mattress 1 9 and the second nurse pulls free the soiled pad, cleans the mattress cover and unrolls the clean pad. She also tucks the remaining part of the underlie extension under the head pad 22 and tucks the unrolled flap under the mattress 19.

The above procedure is similar to the typical drawsheet changing procedure but is easier to accomplish.
Referring again to the arrangement of Figures 1, 2 and 3, the flaps 24, 24', 14, 14', 25 and 25' of the pads 23, 11 and 22 are arranged so as to avoid tensioning the mattress surface where the heavy and/or prominent parts of the body are normally positioned. This reduces pressure levels on the bony prominences which are most likely to be the site of pressure sores (ie the sacrum, hips and heels). Being positioned at the head end of each pad, the flaps are also able to anchor the central and foot pads 11 and 23 more effectively against the considerable shearing forces which develop when patients sit up in bed. It is a particular feature of the embodiment described so far, that the side flaps project from the main portion of the sheet member at an angle other than 90°. Referring for example to the sheet member 11 in Figure 1, the flap 14 projects from the main portion 12 and underlie portion 13 in such a way that the longer side of the flap 14 facing towards the foot of the bed (indicated at 14A) makes an angle of 120° with the side edge of the main portion 12. Thus the flap 14 projects not only outwardly relative to the main portion 12 but also longitudinally towards the head of the bed. In other embodiments this angle between the side 14A of the flap 14 and the side of the main portion 12 may be other than 120°, and may be preferably in the range 100° to 140°, most preferably in the range 110° to 130°. In Figure 1 a there is shown a modification of the flaps 14 and 14' shown in Figure 1. The modified flap is shown at 15 and has a side 15B at the head end of the flap 15, a side 15A positioned at the foot end of the flap 15, and a rolled side edge 1 5C. As shown in Figure 1 a the flap 15 is substantially triangular in shape, the foot end side 1 5A making an angle of 90° with the side of the main portion 12, and the head end side 15B making an angle of between 110⁰ to 140° with the side of the main portion 12. In this case the foot end side 15A of the flap 15 is positioned in line with the edge of the main pad portion 12 and the extreme edge 15C of the flap 15 is longer than that shown in Figure 1.
Preferably each of the side flaps (eg 14) terminates in a rolled edge (eg 14C) to assist anchoring of the flap. In some embodiments the width of the flap 14 may be such that the end edge indicated at 14D is the same length as the shorter side of the underlying portion 13, or the end edge 14D may be longer as shown in Figure 1 so as to be secured partly to the underlie portion 13 and partly to the main portion 12.
When the sheet members are used in a so-called "net" suspension bed, the flaps are simply tucked under the pads.
By way of example of dimensions which may be used, the main portion 12 of a sheet member may have dimensions of 990 mm by 740 mm. The underlie portion may be made of material 132 mm wide, including 17 mm for stitching to the main portion 12, and 5 mm for the hemmed edge. The side flaps 14 and 14' are cut at an angle as has been described. The long edges shown at 14A and 14B may be 540 mm, but an extra 30 mm of material is needed for the rolled edge. The short edges shown as 14C of the flaps are 240 mm long, but the actual width of each flap at right angles to its longer edge is 200 mm. In this particular embodiment, if a wider flap material is used (eg 250 mm) this should be attached to an underlie portion which is 25 mm wider than the suggested measurement above (ie 157 mm). As shown in Figure 1, the excess width of the flap 14 beyond the underlie portion is sewn to the side of the main portion 12. The extreme end of each flap may be finished as shown in Figure 1, with the end cut at 60° to the longer edge of the flap indicated at 14B, or it may be cut at right angles to the long edge 14B. In the latter case, the long edge 14B of the flap is 420 mm and the other long edge 14A remains at 540 mm. The rolled edge of each flap is preferably not more than 6 mm in diameter (uncompressed).
In the preferred version of the pad shown, there are eleven lines 40 of quilting stitch running along the pad, and these should be equally spaced. Self binding strips 42 as shown in Figure 1 can be used for the pad edges and are conveniently 25 mm wide. The overall thickness of the main portion of the pad should preferably be 10 mm plus or minus 2 mm. The underlie portion of each pad should be as thin as possible consistent with the required strength.
By way of example of the materials which may be used, the foam core of each pad may be a fire-retardant grade of open-cell flexible polyether foam having a density of about 33 Kg/m³ and a low compression set, that is to say a good fatigue resistance. The foam should be fairly resilient but not so resilient that it fails to stay in a loose roll, as is required when the pads are being changed. However this may be less important if the foam gradually loses resilience upon laundering.
The foam should be such as to withstand repeated hospital laundering without serious loss of hardness/resilience. Ideally, it should be able to stand 200 launderings, the pads being washed in the same way as towels.
The uppermost surface of the pad should have a relatively low friction (preferably slightly lower than the friction of standard hospital sheets), and should contain sufficient cotton/viscose material to absorb fluid excreta. Its absorptive capacity should be similar to that of a good-towel. It should also be a weft-knitted fabric which is pre-shrunk and able to withstand repeated laundering as mentioned above. Thus it is preferred that the pads shown in the drawings have their main portions 12 surfaced by knitted towelling. Any adhesive used for bonding the surfacing material to the foam (as will be described below in an alternative method of construction) must be porous.
The backing of each main portion is made from the same material as the uppermost surface so that any shrinkage due to laundering will not result in the pad curling or bowing.
If the material used for covering the foam core has dissimilar surfaces (as may be the case with towelling) it is best that the smooth surface is used on all the outside surfaces of the pad.
The flaps of each pad should be made from a material which is both strong and has a high coefficient of friction, when matched with the various mattress cover materials it is likely to encounter.
The rolled edge of each flap may contain a thin strip of polyether foam, to give improved anchorage under the mattress. The material of the flaps should also be hygroscopic, although a synthetic material which is unlikely to cause high static electric charges (when used in conjunction with polyurethane or nylon mattress covers) would be acceptable.
The underlie portion of each sheet member should be a smooth woven material which is also absorbent, ordinary cotton sheeting being preferred.
In the preferred form shown in Figures 1 to 4, each pad is constructed by stitching the foam core to the uppermost layer and the backing with a continuous quilting stitch. This longitudinal quilting (down the bed) holds the foam core in place, without bonding being needed, and also makes it easy for the nurses to align the pads correctly when they are positioning them on a bed.
In an alternative construction (not shown in the figures) the uppermost layer and backing material are bonded to the two sides of the foam core with a porous adhesive. Both constructions can be produced by a continuous process with the foam roll and the two material rolls all being 990 mm wide.
On the quilted type of construction, the surfacing material should be aligned so that the quilting stitch is aligned with the weft of the material, so as to avoid excessive stretching of the fabric between the lines of quilting due to shear forces when patients are seated in bed.
Once the continuous laminate has been produced by either method, it is cut into 740 mm wide pads, and the cut edges are bound using self-binding edging 42, and stitching 43. The binding 42 is the same material as the pad surfacing material, as this ensures that there is no sudden change in friction characteristics of the uppermost surface of the pads. Alternatively, all edges of the pad are secured with an "overlock" stitch.
Any stitching showing on the pad surface should be minimal. The hemmed edge of the underlie portion is kept as shallow as possible.
The high friction side flaps are prepared separately. The flaps may be stitched to the sides of the pad at the same time that the pad sides are finished, suitably using a safety overlock stitch. The indelible line 41 previously mentioned is marked to line up with the edge of the main portion 12 where it joins the underlie portion 13 (in the example shown in Figure 1) and as an alternative this line may be replaced by a coloured stitch line on the flaps. If the flaps are triangular, as described hereinbefore, no indelible folding line is required.
The foam core of the pads eliminates the need for ironing the sheet members of the assembly, and also resists creasing and crumpling due to side forces, as the patient moves about on his mattress.
There will now be described with reference to Figures 5 to 7 an alternative embodiment of the invention. In general, corresponding elements shown in the embodiments of Figures 1 to 4, and Figures 5 to 7, are indicated by like reference numerals.
In Figure 5 there is shown in perspective view a single sheet member 11 and the main portion 12 is formed of an upper layer 16 of stretch towelling bonded to an inner layer 17 of polyether foam which in turn is covered by a layer 18 of backing material. The backing material 18 continues to form the underlie portion 13 which is thus of lesser thickness than the thickness of main portion 12. The flaps 14 and 14' are made of high friction material for tucking under the mattress to secure the sheet member 11. As has been described with the embodiment of Figures 1 to 4, a mattress 19 is covered by three sheet members 11, 22 and 23, the sheet members 22 and 23 being of identical construction to the sheet member 11. The sheet member 22 is positioned at the head of the bed (relative to the position of an occupant of the bed, shown by way of example at 20 in Figure 6), and the sheet member 23 is positioned at the foot of the bed.
The three sheet members 11, 22 and 23 are positioned across the mattress adjacent to one another with the underlie portion 26 of sheet member 23 underlying part of the sheet member 11 and the underlie portion of the sheet member 11 underlying part of the sheet member 22. As shown in Figure 6, the side flap 14 of the sheet member 11 is tucked under the mattress 19 as is the side flap 14' (not shown). The side flaps of the sheet member 23 (of which one is indicated at 24) are tucked in similar fashion under the mattress 19.
The folding of the head sheet member 22 is arranged differently from the sheet members 11 and 23. The side flaps of the sheet member 22 are indicated at 25 and 25' and the underlie portion is indicated at 27. In fact for the end sheet member the underlie portion is not arranged to underlie another sheet member, but instead is tucked under the mattress along the short, head side of the mattress. The side flaps 25 and 25' extending from the underlie portion 27 are then folded back upwardly along the sides of the mattress 19 and are tucked under the main portion of the sheet member 22 (the main portion being indicated at 28).
One of the main differences between the embodiment of Figures 5 to 7 and the previous embodiment, is that the flaps eg 14 and 14', extend laterally at right angles to the sides of the remainder of the sheet member and the edges of the underlie portion are angled. However, because the flaps are positioned at the head end of each pad, the flaps are still able to anchor the central and foot pads 11 and 23 more effectively against the considerable shearing forces which develop when patients sit up in bed. Construction details of this embodiment differ from the preferred embodiment in that the backing material 18 is not bonded to the main pad 12 but is stitched to the uppermost layer of towelling 16 where this is extended around the main pad 12 at the head end and foot end edges. Such a construction avoids stitching on the main pad (uppermost) surface, but does not facilitate commercial production of the sheet member.
In order to comply with safety requirements, the following features should preferably be present. The materials used should have a low flammability, especially the surface towelling material. All materials used should be hypoallergenic and non-toxic. No coloured fabrics should be used, unless these are pastel shades which will withstand bleaching. The pads should be capable of disinfection by an approved method. These safety requirements apply to both embodiments described with reference to the drawings.

Claims

1. A sheet member (11) for combination with two other sheet members (22, 23) to form a sheet assembly for a mattress, said sheet member (11) having dimensions adapted for the sheet member (11) to be positioned transversely across a single bed mattress (19) of conventional shape and size to provide a covering for part of the length of the mattress (19), said sheet member (11) being formed by a member (11) which is a substantially flat planar member when not in use on a mattress, said sheet member (11) comprising a main portion (12) adapted to provide a contact surface for a user (20) of a mattress (19) on which the sheet member (11) is used, characterised in that said sheet member (11) comprises an underlie portion (13) of smaller area than said main portion (12) and adapted for underlying part of another sheet member (22) when in use on a mattress (19), said underlie portion (13) having a thickness less than the thickness of said main portion (12), and side flaps (14, 14') extending laterally from the sides of said sheet member (11) at or in the region of the said underlie portion (13) for retaining said sheet member (11) in position on a mattress (19).

2. A sheet member according to Claim 1 in which said sheet member (11) has on each side thereof a side flap (14, 14') which, when laid coplanar with the remainder (12, 13) of said sheet member (11), has at least a portion (14B, 15B) which extends laterally at an angle of inclination to the side of said sheet member (11).

3. A sheet member according to Claim 1 or 2 in which said main portion (12) of said sheet member (11) comprises an upper covering layer (16) providing said contact surface, a layer (17) of synthetic plastics foam or other washable cushioning material, and a bottom layer (16') of backing material.

4. A mattress assembly comprising a mattress (19), a first sheet member (22) positioned transversely across the mattress (19) at the head of the mattress (19), a second sheet member (11) positioned transversely across the mattress (19) at a position intermediate the head and the foot of the mattress (19), and a third sheet member (23) positioned transversely across the mattress (19) at the foot of the mattress (19), each said sheet member (22, 11, 23) comprising a main portion (12, 28) adapted to provide a contact surface for a user (20) of a mattress (19) on which the sheet member (11) is used, characterised in that said first, second and third sheet members (22, 11, 23) are of substantially identical size, shape and construction, and each sheet member (22, 11, 23) is formed by a member which is a substantial flat planar member when removed from said mattress (19), each said sheet member comprising an underlie portion (13, 26, 27) of smaller area than said main portion (12, 28) and adapted for underlying part of another sheet member when in use on a mattress (19), said underlie portion having a thickness less than the thickness of said main portion, and side flaps (14, 14', 24, 25') extending laterally from the sides of said sheet member at or in the region of the said underlie portion for retaining said sheet member in position on a mattress (19), said first sheet member (22) being positioned with said underlie portion (27) thereof and part of said main portion (28) thereof folded to leave only part of said main portion (28) exposed on top of said mattress (19), said second sheet member (11) being positioned with said underlie portion (13) thereof underlying part of said main portion (28) of said first sheet member (22), and with said main portion (12) of said second sheet member (11) closer to the head of the mattress (19) than to the foot of the mattress (19), and said third sheet member (23) being positioned with said underlie portion (26) thereof underlying part of said main portion (12) of said second sheet member (11).

5. A mattress assembly according to Claim 4 in which each sheet member (22, 11, 23) has on each side thereof a side flap (14, 14', 24, 25) which, when laid coplanar with the remainder (12, 13, 26, 27, 28) of the sheet member, has at least a portion (14B, 15B) which extends laterally at an angle of inclination to the side of the sheet member.

6. A mattress assembly according to Claim 5 in which said main portion (12) of each said sheet member (11) comprises an upper covering layer (16) providing a contact surface for a user of the mattress assembly, a layer (17) of washable cushioning material, and a bottom layer (16) of backing material.

7. A mattress assembly according to Claim 4, 5 or 6 in which said first sheet member (22) is positioned with said underlie portion (27) thereof and part of said main portion (28) thereof folded around the head of the mattress (19) to leave only part of said main portion (28) exposed on top of said mattress, said underlie portion (27) of said first sheet member (22) being positioned under said mattress (19), and at least part of each side flap (25, 25') leading upwardly from said folded part of said first sheet member (22) and being tucked between the top of said mattress and said exposed part of said first sheet member (22) which is on top of said mattress (19), said second sheet member (11) being positioned with said side flaps (14, 14') of said second sheet member (11) leading downwardly and being tucked under said mattress (19), and said third sheet member (23) being positioned with said side flaps of said third sheet member (23) leading downwardly and being tucked under said mattress (19).

8. A method of making a bed comprising the steps of positioning across a mattress (19) three sheet members (22, 11, 23) to provide a covering over the mattress for a user (20) of the mattress to lie or sit on, characterised by the steps of positioning transversely across said mattress (19) at the head of the mattress a first sheet member (22) according to Claim 1,2 or 3, folding said underlie portion (27) of said first sheet member (22) and part of said main portion (28) of said first sheet member (22) so as to leave only part of said main portion (28) of said first sheet member (22) exposed on top of said mattress (19), positioning transversely across said mattress at a position intermediate the head and the foot of the mattress a second sheet member (11) also according to Claim 1, 2 or 3, and substantially identical to the first sheet member (22), arranging said second sheet member (11) with said underlie portion (13) thereof underlying part of said main portion (28) of said first sheet member (22), and with said main portion (12) of said second sheet member (11) closer to the head of the mattress (19) than to the foot of the mattress, positioning transversely across said mattress at the foot of the mattress a third sheet member (23) also according to Claim 1, 2 or 3, and substantially identical to the first sheet member (22), and arranging said third sheet member (23) with said underlie portion (26) thereof underlying part of said main portion (12) of said second sheet member (11).

9. A method according to Claim 8 including the steps of tucking around the sides of said mattress (19) said side flaps (14, 14', 24, 25) extending laterally of each said sheet member (22, 11, 23) so as to retain each said sheet member (22, 11, 23) on said mattress (19).

10. A method according to Claim 9 including the steps of folding said underlie portion (27) and part of said main portion (28) of said first sheet member (22) around the head of said mattress (19) so as to position said underlie portion (27) of said first sheet member (22) under said mattress (19), and lifting part of each side flap (25) of said first sheet member (22) upwardly from said folded part of said first sheet member (22) and tucking said part of said side flap (25) between the top of said mattress (19) and said exposed part (28) of said first sheet member (22) which is on top of said mattress (19).