Abstract: A process for producing a foamed polymer comprises the steps of: mixing, in a dissolver, a mixture constituted by at least one isocyanate and a first unsaturated anhydride, which is charged to the dissolver in the liquid state and at a relatively high temperature; progressively cooling said mixture, with continued stirring, until a temperature not higher than 22.degree. C. is reached; adding to the mixture, with the latter being still kept with continuous stirring, a second unsaturated anhydride, at least one foaming agent, a vinylidene compound, poly(vinyl chloride) and a heat stabilizer; maintaining the mixture with continuous stirring, at said temperature, until a paste is obtained which is poured, after being preliminarily filtered, into a mould or container; curing said paste by charging the container to an oven at atmospheric pressure, and at a temperature not higher than 80.degree. C.; completing the curing of the paste-like mixture under pressure, by increasing temperature up to 180.degree. C.