Open celled cellular polyurethane products

Process for making open celled polyurethane foam suitable for use as insulating or structural material comprising the step of reacting an organic polyisocyanate with a polyfunctional isocyanate-reactive composition in the presence of an isocyanate-reactive cyclic compound of formula (I) ##STR3## wherein Y is O or NR' wherein each R' independently is a lower alkyl radical of C.sub.1 -C.sub.6 or a lower alkyl radical substituted with an isocyanate-reactive group;

• each R independently is hydrogen, a lower alkyl radical of C.sub.1 -C.sub.6 or (CH.sub.2).sub.m - X wherein X is an isocyanate-reactive group which is OH or NH.sub.2 and m is 0, 1 or 2;
• and n is 1 or 2;
• with the proviso that at least one of R' or R is an isocyanate-reactive group;
• wherein the reaction is carried out in the presence of a cell opening agent selected from the group consisting of fatty acids, fatty acid amines, fatty acid amides and fatty acid esters.