| http://www.w3.org/ns/prov#value | - Where a film is used the film may be a single film, or a laminated film such as disclosed in GB-A-2,244,258.The thickness of the film may be up to 2 mm, more preferably up to 1 mm, more preferably 40 to 300 ??m, more preferably 60 to 200 ??m, especially 60 to 160 ??m, more especially 60 to 150 ??m.The film may be produced by any process, for example by extrusion and blowing or by casting.
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