The instant invention is directed to a process for the production of cold setting, flexible foams which contain urethane groups by the reaction of polyethers with a molecular weight of 400 to 10,000 which contain at least two hydroxyl groups and in which at least 10% by weight of the hydroxyl groups are primary hydroxyl groups, with a mixture of diphenyl methane diisocyanates and oligomeric polyphenyl-polymethylene polyisocyanates in the presence of blowing agents and optionally in the presence of catalysts and other foaming aids, the improvement wherein the mixture of diphenyl methane diisocyanates and polyphenyl-polymethylene polyisocyanate mixtures is substantially free of carbodiimide groups, has an isocyanate content greater than 30%, and contains from 60 to 90% by weight of 4,4' diphenyl methane diisocyanate and from 3 to 30% by weight of 2,4' diphenyl methane diisocyanate.