EP1893505A2

EP1893505A2 - Insulating material

Info

Publication number: EP1893505A2
Application number: EP06744341A
Authority: EP
Inventors: Stephen c/o GASM Ltd TEW; Henrik c/o GASM Ltd HESS-PETERSEN
Original assignee: General Applications for Special Materials Ltd
Current assignee: General Applications for Special Materials Ltd
Priority date: 2005-06-03
Filing date: 2006-06-02
Publication date: 2008-03-05
Also published as: WO2006129130A2; WO2006129130A3

Abstract

A material (1) comprising a plurality of closed cells (5) is provided, the space within each cell being substantially evacuated. This may be achieved by sealing a dimpled film (2) to a sealing film (4) in a vacuum so that each dimple (3) is closed while under vacuum to form an evacuated closed cell.

Description

INSULATING MATERIAL

Field of the Invention

The present invention relates to insulating material and in particular, though not necessarily, to a lightweight thermally insulating material suitable for use in the manufacture of containers such as drinks containers, and in food packaging.

Background to the Invention

Consumers are used to purchasing ready-made drinks in either metallic, glass, or plastic containers. Metallic containers are typically of the "can" type having an open only mechanism such as a ring-pull, whilst glass and plastic containers are typically in the form of a bottle with a screw on lid. Of the various materials, metal might be considered the most preferred, firstly because it gives the drinker the best perceived taste, secondly because the materials used are generally recyclable, and thirdly because metallic containers are in practice unbreakable. Glass might be considered the second choice material because it is both recyclable and gives a good taste sensation, with the disadvantage that glass containers are breakable. Plastic might be considered the third choice material because of the perceived poor taste quality which it provides.

A problem with a standard beverage container is that, after removal from a cold storage environment, the temperature of the liquid within the container starts to rise due to heat transfer with the external environment. In the case of most soft drinks, this is undesirable. The problem is particularly acute in the case of metallic containers as the metal walls conduct heat rapidly into the interior space.

There are many occasions when it would be desirable to keep food at a stable temperature. For example, when chicken is bought from a supermarket, it is removed from a refrigerated display cabinet, placed in a trolley, taken outside, placed in the boot of a car, and then (perhaps an hour later) placed into a fridge. The temperature of the chicken fluctuates considerably, potentially providing suitable conditions for the growth of bacteria. If the chicken could be maintained at a constant temperature this would greatly reduce the associated health risk.

Metallic beverage cans having improved thermal insulating properties are known in the prior art. For example, JP 3254322 describes a dual tube construction can body, the space between the two tubes being either evacuated or filled with a heat insulating material. US 6,474,498 describes a container having an outer can and an inner liner of "bubble wrap" material. However, the known improved cans suffer from a number of disadvantages including: high cost, insufficient thermal insulation, poor recycleability, difficulty of manufacture, and an inability to cope with a pressurised content.

An insulating material is known from WO 98/07780 and DE 69819365T2 which comprises particles of aerogel embedded within a plastics matrix for moulding as an insert or for spray coating.

Summary of the Invention

In accordance with one aspect of the present invention there is provided a material comprising a plurality of closed cells, the space within each cell being substantially evacuated.

Preferably, the material comprises a dimpled film having a plurality of dimples protruding from a front side thereof, and a sealing film sealed to a reverse side of the dimpled film between the dimples, so that each dimple is closed by the sealing film to form one of the closed cells.

The films may be formed of a plastics material. In a preferred embodiment the films are made from a polymer such as polyethylene terephthalate (PET). In order to improve the vacuum retention properties, one or both of the films is preferably coated with a metal layer. If both are coated, the seal between the films may be a molecular seal between the metal layers. Alternatively, the seal may be a heat seal. The metal may be aluminium, for example.

The dimples may be any suitable shape, but in one preferred embodiment they are substantially hemispherical.

In one embodiment, a second sealing film is sealed to the top of each dimple so that the spaces between the dimples are closed to form further substantially evacuated closed cells. This may be facilitated if each dimple has a substantially flat top. The dimples may be tessellated such that the spaces between the dimples are substantially the same size as the internal spaces of the dimples.

Alternatively, in one embodiment a "double layer" material is provided, having a second dimpled film sealed to a second sealing film in a similar manner to that described above, the two dimpled films being located adjacent one another with their front sides facing each other so that the dimples interlock. The edges of such a material may be sealed, enabling the spaces between the interlocking dimples to be substantially evacuated.

The sealing film itself may have dimples formed therein, which may correspond to the dimples of the dimpled film and extending in the opposite direction. This arrangement enables larger cells to be formed simply.

In another embodiment, the material comprises a shaped layer defining an array of cells, and at least one sealing layer sealed to at least one side of the shaped layer, so that each cell is closed by the sealing layer or layers. Each cell may be substantially hexagonal.

The pressure in each closed cell is preferably less than about 10^"3 mbar, more preferably less than about 10^ mbar. The material preferably comprises a reflective layer. This may be formed, for example, of silver. The material is preferably formed as a sheet, which may be flexible.

The invention also provides a beverage container comprising a sheet of material as described above. Typical beverage containers in which such material may be used include rigid cans and flexible pouches. The invention also provides a sheet of insulating material suitable for use in food packaging. A further embodiment provides a sheet suitable for decorating the walls or ceilings of a building.

The material of the invention may also include elements which must be kept under vacuum inside the closed cells. Such elements may include data storage devices and/or trapped radiation or atoms.

In accordance with another aspect of the present invention there is provided an insulating material, comprising a shaped film comprising a plurality of self-supporting pockets extending from a front side thereof, and a sealing film sealed to a reverse side of the shaped film between the pockets, so that each pocket forms a closed cell, each closed cell being substantially evacuated.

In accordance with a further aspect of the present invention there is provided an insulating sheet comprising an array of substantially evacuated, self-supporting closed cells.

In accordance with a yet further aspect of the present invention there is provided an insulating material comprising a plurality of substantially evacuated closed cells separated from each other by thin walls

In accordance with another aspect of the present invention there is provided a method of manufacturing a material, comprising providing a dimpled film having a plurality of dimples protruding from a front side thereof and, in a vacuum, sealing a sealing film to a reverse side of the dimpled film between the dimples, so that each dimple is closed by the sealing film to form a substantially evacuated closed cell.

Thus, by sealing the dimples under vacuum to form closed cells, the vacuum is "locked in" to the cells so that the cells remain evacuated when the material is removed from the vacuum chamber.

The dimpled film may be formed by stamping a blank film of, for example, a plastics material. A preferred material is a polymer such as polyethylene terephthalate.

The dimpled film and sealing film are preferably coated with metal, for example aluminium. The metal preferably coats the inside of each dimple, to improve the vacuum-holding characteristics. The step of coating with metal is preferably performed under vacuum, and in a preferred embodiment the steps of coating the films with metal and sealing the sealing film to the dimpled film are performed in the same vacuum chamber. The step of coating with metal may include passing a current through the metal, vaporising it and spraying it onto the films.

The step of sealing preferably includes providing a positive charge to one of the films and a negative charge to the other of the films so that the metal coatings seal to each other by molecular attraction.

A second sealing film may be sealed to the tops of the dimples under vacuum. The edges of the material may then be sealed under vacuum so that the spaces between the dimples remain evacuated when the material is removed from the vacuum.

In accordance with a further aspect of the present invention there is provided a method of manufacturing a material, comprising forming a shaped layer defining an array of cells and, under vacuum, sealing at least one sealing layer to the shaped layer on at least one side so that each cell is closed by the sealing layer or layers while under vacuum. An element may be inserted into some or all of the cells before the sealing layers are sealed to close the cells. This provides a particularly useful way of storing small elements which must be kept under vacuum. A data storage device, for example, may be an element which could usefully be placed into one of the cells before sealing. Radiation or atoms may be trapped in one or more of the closed cells before sealing.

In accordance with a yet further aspect of the present invention there is provided a method of manufacturing a material, comprising: forming a dimpled film having a plurality of dimples protruding from a front side thereof, each dimple linked to each other dimple by a pathway; sealing a sealing film to a reverse side of the dimpled film between the dimples, so that each dimple is substantially closed by the sealing film, but with each dimple still linked to each other dimple by the pathways so that gas can travel between the dimples; evacuating the substantially closed dimples by placing the films in a vacuum; and closing the pathways between the dimples with the films still under vacuum so that each dimple forms a substantially evacuated closed cell. The pathways may be closed by stamping the dimpled film.

This aspect enables the layers to be sealed together at atmospheric pressure. The material can then be placed in a vacuum so that all the cells are evacuated via the pathways between them. If these pathways are closed while the material is under vacuum, the vacuum will again be "locked in" to each closed cell when the material is removed from the vacuum.

Brief Description of the Drawings

Some preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 illustrates a thermally insulating material;

Figure 2 is a cross-sectional view of the thermally insulating material of Figure 1; Figure 3 illustrates a process for manufacturing the material of Figure 1 ;

Figure 4 is a cross-sectional view of an alternative insulating material; Figure 5 illustrates a process for manufacturing the material of Figure 4; Figure 6 illustrates an alternative process for manufacturing the material of Figure 1; Figure 7 is a cross-sectional view of a double layer insulating material; Figure 8 is a cross-sectional view of an alternative double layer insulating material; Figure 9 illustrates a process for manufacturing another alternative insulating material; Figure 10 is a plan view of a partially formed insulating material; Figure 11 is a cross section of an insulated beverage can; Figure 12A is a plan view of a cardboard carton; and

Figure 12B is a plan view of the carton of Figure 12A coated in an insulating material.

Detailed Description of Certain Embodiments

Figure 1 is a schematic view of a thermally insulating material 1. The material is made from a film 2 of a mouldable material such as polyethylene terephthalate (PET), in which is formed an array of hollow "bubbles" or dimples 3 extending away from one side of the film 2. A sealing film 4 is sealed to the back of the film 2 between the dimples. Each dimple thus forms an airtight closed cell 5. The interior of each cell 5 is evacuated so that the air pressure inside the cell is less than 10^ mbar.

Figure 2 is a cross section through the material 1 of Figure 1, illustrating further details of construction. A metal coating 6 is deposited on the back of the dimpled film 2, so as to coat the inside of the dimples 3 and the regions 7 between them. Another metal coating 8 is deposited on the front of the sealing film 4. A suitable metal for these coatings is aluminium. The metal coatings improve the impermeability of the cells 5 to air or other gases, by substantially preventing diffusion through the films.

At the regions 7 between the dimples 3, the film 2 and sealing film 4 are sealed to each other to ensure that the interior of the dimples 3 form closed cells. The seals 7 may be formed by heat sealing, or more preferably by a molecular bond between the metal coatings 6, 8. A molecular bond provides an exceptionally strong and airtight bond between the two films 2, 4. Figure 3 is a schematic illustration of a method suitable for manufacturing the material of Figures 1 and 2. The film 2 is initially wound on a roller 10. The roller 10 is placed in a vacuum chamber 11, which is evacuated to a pressure of less than 10^ mbar. Another roller 12 has the sealing film 4 wound thereon, and this is also unwound within the vacuum chamber 11. The sealing film 4 and film 2 are passed between a heated roller 13 and a profiled roller 14, having surface indentations matching the dimples 3 on the film 2. The heated roller 13 and profiled roller 14 supply pressure towards each other so as to press the film 2 and sealing film 4 together to form a seal between the dimples 3. Since this operation is carried out under vacuum, the dimples 3 contain a vacuum when the seal is made. The vacuum is thus "locked in" to the closed cells 5 formed by the dimples. When the material is removed from the vacuum chamber, the closed cells 5 will remain evacuated.

A metal deposition system is also provided inside the vacuum chamber 11. This comprises a metal source 15. The source 15 is heated and a current passed through it, causing the metal to vaporise. The vaporised metal 17 coats the film 2 and sealing film 4 to form the layers 6, 7 shown in Figure 2.

In order to form a molecular seal between the two coatings 6, 8, a positive or negative charge is applied to the film 2, for example by applying a charge to the roller 10. An opposite charge is applied to the sealing film 4, for example by applying the charge to the heated roller 13. When pressure is applied between the heated roller 13 and profiled roller 14 to form the seal in the regions 7 between the dimples, the positive and negative charges on the two films 2, 4 cause the metal coatings 6, 8 to attract each other, and this leads to the formation of the molecular seal between the two coatings.

Once the seal has been made, the material is passed over another roller 19 and wound onto a storage roller 20. It can then be removed from the vacuum chamber ready for use. The evacuated closed cells 5 do not allow thermal conduction therethrough, and thus provide effective thermal insulation. Although the cells 5 are coated with a metal layer 6, this is only a few nm thick and does not provide an effective conducting path for heat.

It will be appreciated that other layers (not shown) may also be applied to the material. For example, a silvered layer may be applied on one or both sides of the material 1 in order to prevent radiative heat transfer. This layer may be applied in the vacuum chamber 11 or outside. Similarly, printed layers and films designed to contact air or liquids may also be applied to provide a required "finish" to the material. Where the material is used in food or drink packaging, a layer of polyvinylidene chloride (PVDC) may be applied on the side contacting the food or drink.

Figure 4 is a cross section of an alternative insulating material 21. The material is similar to the material 1 shown in Figure 2, but the metal coating 8 applied to the sealing film 4 is applied to the side facing away from the dimples 3. In this alternative, the seals 7 between the dimples are formed by heat moulding the plastic of the sealing film 4 to the metal coating 6 on the film 2.

Figure 5 illustrates a method by which the insulating material 21 shown in Figure 4 may be manufactured. The method is similar to that shown in Figure 3, except that the metal source 26 for supplying vaporised metal 28 to the sealing film is located so that the metal coating is applied after the films 2, 4 have passed between the heated and profiled rollers 13, 14.

It will be appreciated that further variations of metal coating are also possible. In some embodiments it may not be necessary to include any metal coatings, as long as the material used for the film 2 and sealing film 4 is sufficiently impermeable to air. Alternatively, the coatings may be deposited on the outside of the dimples, or on both sides of either or both films 2, 4. If suitable materials are used, it may be appropriate to use a metal film without a plastic layer, especially for the sealing film 4. Similarly, the molecular or metal-to-metal seal may be replaced by any suitable sealing mechanism capable of creating an airtight seal. Suitable examples include radio frequency sealing, heat sealing, foil induction heating, foil induction sealing, adhesives, or static charging.

Figure 6 illustrates an alternative method for manufacturing the material 1 of Figure 2. The method is similar to that shown in Figure 3, except that the film 2 is stored on a roller 30 before the dimples 3 are formed therein. The film 2 passes over an aligning roller 31 and through a stamp press 32 which presses the dimples into the film 2. The film 2 is then sprayed with metal 17 and sealed to sealing film 4 as described with reference to Figure 2. It will also be appreciated that the stamp press 32 could be replaced by a pair of profiled rollers, for example.

Figure 7 is a cross section through a "double layer" insulating material 41. The material is formed by two layers of material 1, similar to that shown in Figure 2, placed opposite each other so that the dimples interlock. It can be seen that a significant portion of the volume between the two sealing layers 4 is taken up by the evacuated cells 5, thus increasing the insulating properties of the material. To improve the insulating properties still further, the two materials 1 may be sealed or welded to each other 43 around the edges while the material is still under vacuum. This ensures that the spaces 44 between the closed cells 5 are also evacuated, improving the insulating properties still further. The dimples of each film may be tessellated in a suitable fashion to occupy the most space between the two sealing films 4. Suitable tessellations include square or hexagonal patterns.

Figure 8 is a cross section through another alternative insulating material 51. In this embodiment, the sealing film 52 has itself been formed with dimples 53, corresponding to the dimples 3 of the film 2. The corresponding dimples 3, 53 extend in opposite directions to form a closed cell 5 when the regions 7 between the dimples 3, 53 are sealed. In this example, the film 2 and sealing film 52 have been shown with metal coatings 6, 56 on the inside, with a metal to metal seal in the between-dimple regions 7, but it will be appreciated that other seals may be used, as described above. The method of manufacture may involve two profiled rollers similar to the profiled rollers 14 shown in Figures 3, 5 and 6. Alternatively, static profiled stamps may be used to press the between-dimple regions 7 together. It will be appreciated that two layers of material 51 may be placed adjacent to each other to form a double layer material.

In all of the examples described above, the dimples are shown in the figures as being substantially hemispherical. This shape has the advantage that it is structurally robust, and able to withstand external pressure when evacuated without collapsing. In addition, hemispherical dimples are suitable for forming a double layer interlocking material, as shown in Figure 8. However, other dimple shapes may be used. If flat-topped dimples are used, it may be possible to seal an additional sealing film 64 to the opposite side of the material.

Figure 9 illustrates a suitable method for forming an insulating material having a dimpled film 2 sandwiched between two sealing films 4, 64. The film is initially wound from a roller 10 in a vacuum chamber 11 and stamped using a press stamp 62 to form dimples 3. The dimples 3 are flat topped. Both sides of the dimpled film 2 are coated with metal from heated metal sources 65, 66. The coated film 2 then passes between two heated rollers 13, 63, over which pass sealing films 4, 64. The sealing films are themselves metal coated from metal sources 67, 68. As with the other methods previously described, the film 2 is charged oppositely to the sealing films 4, 64 so that the metal coatings form molecular seals. Alternatively, other seals may be produced as described previously.

Seals are formed above and below the dimples while still under vacuum, so that the dimples 3 form closed cells, and the space between the dimples is also evacuated. If the edges of the dimples are arranged to contact each other or are linked, the spaces between the dimples will themselves form closed cells, each of which will remain evacuated when the material is removed from the vacuum. Thus virtually the whole of the interior of the material will be evacuated. If the dimples are individual, unlinked, shapes, it will be necessary to weld around the edges of the material while still under vacuum to ensure that the space between the dimples 3 remains evacuated. Suitable patterns for flat-topped dimples include hexagonal tessellations and square tessellations.

Figure 10 is a plan view of a dimpled film 2 for use in an alternative method of manufacture of an insulating material. The dimples 3 are linked by pathways 72 which allow gas to move between the dimples. The film 2 is sealed to a sealing film (not shown), and this sealing may or may not be done under vacuum, since the pathways remain open once the sealing is complete.

The sealed material may then be placed in a vacuum, thus enabling all of the dimples 3 to be evacuated at once via the pathways 72. A stamp press or profiled roller may then be used to press down on the pathways 72 so as to close them, closing each of the dimples 3 to form evacuated closed cells.

The materials described above may be exceptionally thin by the usual standards of insulating material. The plastic films are of the order of a few microns in thickness, and the metal coatings (if used) no more than a few nm. The dimples and closed cells may be of the order of 1 mm from top to bottom, so the material can be 1 mm thick or less.

Figure 11 is a cross section through a typical beverage can 81. The cylindrical wall around the can 81 has been lined with an insulating material 82, which may be any of the insulating materials described above. In the example shown, the material is only provided around the edge of the can, as in practice this is where most heat enters the can. However, if necessary, the insulating material may be placed over the bottom of the can. For aesthetic reasons, it is preferred that the insulating material 82 is placed inside the can but it will be equally effective around the outside. Figure 12A is a plan view of a typical cardboard carton 83 used to store liquids such as milk and the like before assembly. Figure 12B shows the same carton lined with insulating material 84 described above, with the dimples 3 clearly visible. When such a carton is assembled, it will keep the milk at a constant temperature for a much longer period of time than conventional cartons.

It will be appreciated that a thin, flexible insulating material has many applications. It can be used to keep cold items cold, and also to prevent items getting cold. Typical applications include food packaging; beverage cans; bottles; flexible beverage pouches; medical packaging (e.g. for vaccines); containers of any other type; lining for the outside of battery cells; clothing; tents; wallpaper; confectionary wrappers; lining for plasterboards, woodboards, cement fibre boards etc. on the inside or outside; lagging or lining pipes; lining bricks (e.g. on the inside); lining swimming pools; swimming pool covers; lining for heat shrinking; roof insulation; lining metal, glass, ceramic, or wood; lining to provide soundproofing; lining for placing around trees or bushes; lining for magnetic uses; survival blankets; survival rafts. This list is not intended to be exhaustive and the skilled person will be able to think of other applications.

Another application for such a material may be the storage of small elements which must be kept in a vacuum. For example, there are small data storage devices which must be kept under high vacuum. Such devices could be inserted into the cells of the materials described above before they are closed, and would then be stored in small vacuum "pockets". Similarly, radiation or atoms which must be contained under vacuum could be placed into the closed cells.

Claims

CLAIMS:

1. A material comprising a plurality of closed cells, the space within each cell being substantially evacuated.

2. A material according to claim 1, comprising: a dimpled film having a plurality of dimples protruding from a front side thereof; and a sealing film sealed to a reverse side of the dimpled film between the dimples, so that each dimple is closed by the sealing film to form one of the closed cells.

3. A material according to claim 2, wherein the dimpled film is formed of a plastics material.

4. A material according to claim 2, wherein the dimpled film has a metal coating.

5. A material according to claim 2, 3 or 4, wherein the sealing film is formed of a plastics material.

6. A material according to any of claims 2 to 5, wherein the sealing film has a metal coating.

7. A material according to any of claims 2 to 6, wherein the seal between the sealing film and the dimpled film is a heat seal.

8. A material according to any of claims 2 to 7, wherein: the dimpled film has a metal coating on the reverse side; the sealing film has a metal coating on the side facing the dimpled film; and the seal between the sealing film and the dimpled film is a molecular seal between the metal coatings.

9. A material according to claim 4, 6 or 8, wherein the metal in each metal coating is aluminium.

10. A material according to any of claims 2 to 9, wherein the dimples are substantially hemispherical.

11. A material according to any of claims 2 to 9, further comprising a second sealing film sealed to the top of each dimple.

12. A material according to claim 11, wherein each dimple has a substantially flat top.

13. A material according to claim 11 or 12, wherein the dimples are tessellated such that the spaces between the dimples are substantially the same size as the internal spaces of the dimples.

14. A material according to claim 11, 12 or 13, wherein the dimples are tessellated in a substantially hexagonal pattern.

15. A material as claimed in any of claims 11 to 14, wherein the dimples are linked so that the spaces between the dimples are closed by the second sealing film to form further substantially evacuated cells.

16. A material according to any of claims to 2 to 10, further comprising: a second dimpled film having a plurality of dimples protruding from a front side thereof; and a second sealing film sealed to a reverse side of the second dimpled film between the dimples so as to close the dimples to form closed cells; wherein the dimpled film and second dimpled film are located adjacent one another with their front sides facing each other so that the dimples on the dimpled films interlock.

17. A material as claimed in claim 16, wherein the edges of the material are sealed.

18. A material as claimed in claim 17, wherein the spaces between the interlocking dimples are substantially evacuated.

19. A material according to any of claims 2 to 10, wherein the sealing film has a plurality of dimples protruding away from the dimpled film, each dimple of the sealing film corresponding to a dimple on the dimpled film, so that the dimples of the dimpled film and dimples of the sealing film co-operate to form the closed cells.

20. A material according to claim 1, comprising: a shaped layer defining an array of cells; and at least one sealing layer sealed to at least one side of the shaped layer; so that each cell is closed by the sealing layer or layers.

21. A material as claimed in claim 20, wherein each layer comprises metal, and the seals are formed by molecular bonding between the metal in each layer.

22. A material according to claim 20 or 21, wherein each cell is substantially hexagonal.

23. A material according to any preceding claim, wherein the pressure in each closed cell is less than about 10^"3 mbar.

24. A material according to any preceding claim, wherein the pressure in each closed cell is less than about 10^ mbar.

25. A material according to any preceding claim, further comprising a reflective layer.

26. A material according to any preceding claim, the material being formed as a sheet.

27. A material according to claim 26, wherein the sheet is flexible.

28. A beverage container comprising a sheet of material according to any preceding claim.

29. A sheet suitable for decorating the walls or ceilings of a building, the sheet comprising a material according to any of claims 1 to 25.

30. A sheet of insulating material suitable for use in food packaging, comprising a sheet of material according to any of claims 1 to 25.

31. A material according to any of claims 1 to 24, wherein each closed cell contains an element required to be kept under vacuum.

32. A material according to claim 31 , wherein the element is a data storage device.

33. A material according to claim 31 or 32, wherein the element includes radiation or atoms.

34. An insulating material, comprising: a shaped film comprising a plurality of self-supporting pockets extending from a front side thereof; and a sealing film sealed to a reverse side of the shaped film between the pockets, so that each pocket forms a closed cell; wherein each closed cell is substantially evacuated.

35. An insulating material as claimed in claim 34, wherein each of the shaped film and sealing film comprises a metal layer, and the shaped film and sealing film are sealed to each other by molecular attraction between the metal layers.

36. An insulating sheet comprising an array of substantially evacuated, self- supporting closed cells.

37. An insulating material comprising a plurality of substantially evacuated closed cells separated from each other by thin walls.

38. A method of manufacturing a material, comprising: providing a dimpled film having a plurality of dimples protruding from a front side thereof; and in a vacuum, sealing a sealing film to a reverse side of the dimpled film between the dimples, so that each dimple is closed by the sealing film to form a substantially evacuated closed cell.

39. A method according to claim 38, wherein the dimpled film is formed by stamping a blank film.

40. A method according to claim 38 or 39, wherein the dimpled film is a plastics material.

41. A method according to claim 38, 39 or 40, wherein the dimpled film is polyethylene terephthalate.

42. A method according to any of claims 39 to 41, wherein the dimpled film and sealing film are coated with metal.

43. A method according to claim 42, wherein the step of coating with metal is performed under vacuum.

44. A method according to claim 43, wherein the steps of coating the films with metal and sealing the sealing film to the dimpled film are performed in one vacuum chamber.

45. A method according to claim 43 or 44, wherein the step of sealing includes providing a positive charge to one of the films and a negative charge to the other of the films so that the metal coatings seal to each other by molecular attraction.

46. A method according to any of claims 42 to 45, wherein the metal is aluminium.

47. A method according to any of claims 42 to 46, wherein the step of coating with metal includes passing a current through the metal, vaporising it and spraying it onto the films.

48. A method according to any of claims 38 to 47, wherein the sealing film is provided from a roll.

49. A method according to any of claims 38 to 48, further comprising sealing a second sealing film to the tops of the dimples under vacuum.

50. A method according to claim 49, further comprising sealing around the edges of the material under vacuum so that the spaces between the dimples remain evacuated when the material is removed from the vacuum.

51. A method of manufacturing a material, comprising: forming a shaped layer defining an array of cells; and under vacuum, sealing at least one sealing layer to the shaped layer on at least one side; so that each cell is closed by the sealing layer or layers while under vacuum.

52. A method according to claim 51, further comprising inserting an element into one or more cells before closing the cells.

53. A method according to claim 52, wherein each element is a data storage device.

54. A method according to claim 52 or 53, wherein each element comprises radiation or atoms.

55. A method of manufacturing a material, comprising: forming a dimpled film having a plurality of dimples protruding from a front side thereof, each dimple linked to each other dimple by a pathway; sealing a sealing film to a reverse side of the dimpled film between the dimples, so that each dimple is substantially closed by the sealing film, but with each dimple still linked to each other dimple by the pathways so that gas can travel between the dimples; evacuating the substantially closed dimples by placing the films in a vacuum; and closing the pathways between the dimples with the films still under vacuum so that each dimple forms a substantially evacuated closed cell.

56. A method according to claim 55, wherein the pathways are closed by stamping the dimpled film.

57. A method according to claim 55 or 56, wherein each of the dimpled film and sealing film is coated with a metal layer.