Layers 13 and 14 may comprise any metallizable thermoplastic which may include polyolefin resins such as polyethylene, polypropylene, polyisoprene, polybutene, poly-3-methylbutene-1, poly-4-methylpentene-1, polybutadiene, polystyrene and copolymers of constituent monomers of the foregoing polymers (e.g. ethylene/propylene copolymer, linear low density polyethylenes containing butene-1, 4-methylpen