A method of manufacturing multiple-layer molded articles with an outer skin of compact thermoplastic material and a core of foamed thermoplastic material includes initially introducing the material for the skin into a mold cavity in a quantity sufficient for the desired thickness of the skin and subsequently feeding into the mold cavity the material for the core to which the expanding agent has been added. During and/or after being introduced into the mold cavity, the core material containing expanding agent is temporarily subjected by means of an additional gas and/or a pressurized, low-boiling liquid to an active pressure which exceeds the gas pressure of the expanding agent. Subsequently, the additional gas or the low-boiling liquid is removed from the hollow space which is still free of skin material and core material.