A method of producing a heat-sealable sheet or film from polyethylene and isobutylene copolymer for covering an item, comprising:(a) blending in solid form and at elevated temperature, using conventional techniques, a composition comprising a cross-linkable polyethylene, a copolymer of isobutylene and of conjugated diene, said composition having 30 to 70 wt. % polyethylene and 70 to 30% copolymer, together with conventional additives, cooling the resulting blend and granulating said blend in a conventional manner and extruding the granulated particles of said blend through a die to form a sheet or film,(b) irradiating said sheet or film thereby to cross-link the polyethylene,(c) heating said sheet or film to a temperature above its crystalline softening point,(d) stretching said sheet or film and cooling it while stretched so as to maintain the stretched dimension,(e) wrapping said item with said sheet or film,(f) heat sealing the seams of said wrap, and(g) heating said sheet to a temperature above its crystalline softening point thereby to cause contraction of the sheet to its original dimension.
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