a process for producing bodies of polymeric material having an outer shell and a core of foamed material is disclosed . the process includes the steps of : providing a mold having a pair of separable half - molds arranged facing each other ; extruding a tubular thermoplastic parison between the half - molds ; closing the half - molds around the parison , thereby defining a hollow space between the parison and walls of the mold ; injecting into the inside of the parison a thermoplastic polymeric material admixed with a physical blowing agent , the parison expanding into contact with the walls of the mold , and conforming to the shape of the mold ; and removing the article form the mold .