Abstract: In the manufacture of bodies of foamed plastic material, a polymeric synthetic resin base material is mixed with a cross-linking agent, a foaming agent and at least one further additive. The resulting mixture is shaped without a decomposition of the cross-linking and foaming agent and is subsequently heated to effect cross-linking and foaming. In order to obtain bodies of foamed plastic materials which owing to their high flexibility and low flammability are particularly suitable as heat-insulating materials in buildings, the base material consists only of a chlorinated polyethylene resin or a mixture of such resins and heat-stabilizing agents known for use with halogen-containing polymers are incorporated in the mixture.