the present invention concerns an apparatus and process for producing an improved extruded plastic material product which consists of an inner foamed thermoplastic cellular core and an outer non - porous thermoplastic skin extending along at least one side of the core . in the process , a foamable thermoplastic material is extruded through a first die outlet to produce a foamed thermoplastic material . after exiting the die outlet , a film of non - porous thermoplastic material is applied along at least one side of extruded foamed material . next , the extruded foamed material and the non - porous film is fed through a forming die which shapes and seals the materials into the desired cross - sectional shape .