Abstract: An apparatus for the production of injection-molded synthetic-resin bodies having core portions and skin portions of different densities wherein a blowing agent is introduced into the core material to form macroscopic bubbles or cavities therein within the mold and under the molding conditions so that the expanding body of core material presses the skin material against the walls of the mold. The core material is injected coaxially with the skin material but under conditions such that expansion under the effect of the macropore-producing blowing agent does not occur to any significant extent until the core material is within the mold. This is a division of application Ser. No. 507,465, filed Sept. 19, 1974.