Abstract: An expanded polymer product with high distortion temperature, high flame resistance and low smoke toxicity and opacity comprises, in combination:between 18% and 25% of a mixture of at least two isocyanates;between 8% and 11% of a styrene and maleic anhydride mixture;between 19% and 42% of a PVC resin in emulsion form;between 4% and 7% of at least one expanding agent;between 0.5% and 1% of at least one temperature stabilizer;between 16% and 40% of TiO.sub.2.Said product is used particularly in sea, ground and air transport, and in numerous constructional applications in which the materials must combine high technical characteristics with adequate lightness.