Process for the manufacture of highly elastic soft polyurethane foams

In a process of producing cold cure soft polyurethane foams, wherein polyethers having at least two hydroxy groups per molecule, water and organic polyisocyanate are foamed in the presence of catalysts, the foaming system optionally comprising cross-linkers, blowing agents and/or other auxiliaries, the improvement which comprises adding to the foaming system organopolysiloxane of the formula I ##STR4## wherein

• R.sup.1 represents the same of different unsubstituted or substituted hydrocarbon groups which are devoid of groups that have a tendency to enter addition reactions with isocyanate;
• R.sup.2 has the same meaning as R.sup.1 or is OR.sup.3, wherein
• R.sup.3 represents alkyl, aryl, alkaryl or [C.sub.m H.sub.2m O].sub.p R.sup.4,
• R.sup.4 being lower alkyl,
• m = 2 to 4 and
• p being selected such that the mole weight of the total R.sup.3 group does not exceed 400;
• and
• n = 2-10 and wherein essentially none of the individual components of the mixtures possess a value of n>10,
• the amount of the compound of formula I being between about [0,003] 0.003 to 2% by weight calculated on the amount of polyether in the foaming system.