A hat, headband or helmet formed from a material ( 10 ) comprising first and second layers ( 11, 12 ) of material and a low friction interface ( 13 ) arranged between the layers to enable sliding of the first layer of material ( 11 ) relative to the second layer of material ( 12 ).
1. A helmet, comprising a liner formed from a material comprising:
first and second layers of material; and
a low friction interface arranged between the layers to enable sliding of the first layer of material relative to the second layer of material;
wherein at least one of the first and second layers of material are formed from a material that is at least one of a textile, a cloth, a fabric or a felt; and
the at least one of the first and second layers of material is flexible.
2. A helmet according to claim 1 , wherein the at least one of the first and second layers of material is stretchable.
3. A helmet according to claim 1 , wherein at least one of the first and second layers of material is adjacent to the low friction interface.
4. A helmet according to claim 1 , wherein the low friction interface is formed by at least one of the first and second layers of material.
5. A helmet according to claim 1 , wherein the at least one of the first and second layers of material is are formed substantially only from the at least one of the textile, the cloth, the fabric or the felt.
6. A helmet according to claim 1 , wherein the low friction interface comprises a third layer of material, arranged between the first and second layers of material and formed from material selected such that there is low friction between the third layer of material and at least one of the first and second layers of material.
7. A helmet according to claim 1 , wherein low friction interface comprises third and fourth layers of material, arranged adjacent each other between the first and second layers of material, and each formed from material selected such that there is low friction at least between the third and fourth layers of material.
8. A helmet according to claim 1 , wherein the low friction interface comprises a modification of the surface of at least one of the first and second layers such that there is low friction between that surface and an adjacent layer.
9. A helmet according to claim 8 , wherein said modification of the surface comprises the use of a different substance from that used to form the first or second layer of material, impregnated into the surface of the first or second layer of material or bonded to the first or second layer of material.
10. A helmet according to claim 8 , wherein said modification of the surface comprises a physical treatment to the surface of at least one of the first and second layers in order to change the mechanical properties of the surface of the material.
11. A helmet according to claim 1 , wherein the low friction interface is configured such that, under loading that may be expected for apparel being worn by a wearer, the first layer of material may slide relative to the second layer of material.
12. A helmet according to claim 11 , wherein the hat or headband is configured to provide protection to a wearer during an impact; and the low friction interface is configured such that, during an impact that is expected to be survivable for the wearer, the first layer of material may slide relative to the second layer of material.
13. A helmet according to claim 1 , wherein at least one of the first and second layers of material comprises padding.
14. A helmet according to claim 1 , wherein at least one of the layers is perforated.