stable foams at high temperatures

stable at high temperatures foams obtainable by reacting a) at least one organic polyisocyanate with b) at least one organic compound having at least two epoxy groups in such an amount corresponding to a ratio by equivalents of isocyanate groups to epoxide groups of 1.2: 1 to 500: 1, e) optionally in the presence of auxiliaries and additives, characterized in that the reaction is performed in the presence of formic acid as blowing agent and optionally other chemical blowing agents and / or physical T) and a catalyst f) which accelerates the reaction of isocyanate / epoxide.