PURPOSE: To make autoclave sterilization performance by installing an inner layer consisting of polyethylene and outer layer being higher in a melting point than the inner layer and consisting of a plastic film undeteriorated even the specified temperature, while installing a thin film of a metal or metallic compound on a laminate surface of the outer layer, and sealing the inner layers themselves of laminating materials interposing an intermediate layer composed of the specified material between the thin film and the inner layer by means of heating.

CONSTITUTION: Undrawn polyethylene of extremely high molecular weight by a low pressure polymerization process for an inner layer in service is more than one million in viscometric molecular weight, and more than three millions in a light scattering method, so that suchlike value of the molecular weight gives physical properties resistible to a very low temperature. Since it has extremely high melt viscosity, a powder product is formed into a block molding by means of press forming, ram extrusion or the like and then it is used as a desired film of 0.025-0.125mm made by means of planing or the like. This film has high impact resistance in addition to very high molecular weight, and it keeps constant flexibility and good physical properties even under a temperature of -196°C. In addition, since it is very high in melt viscosity, the inner surface is in no case fused even in autoclave sterilization for 30min at 121°C.