Method for the preparation of highly elastic forms of reduced compression hardness having polyurethane groups

A method for the preparation of highly elastic polyurethane foams of reduced compression hardness by the reaction of polyisocyanate with polyether having a molecular weight of 400 to 10,000 and containing at least two hydroxyl groups in the presence of cross-linking agent, catalyst and water and optionally in the presence of emulsifier, stabilizer and organic blowing agent, comprising carrying out the reaction of the polyurethane-forming components in the presence of a compound Y which contains at least one polyoxyalkylene group and at least one group A.sup.- M.sup.30 in the molecule, wherein A is an anionic group selected from the group consisting of --SO.sub.3, --CH.sub.2 CH.sub.2 --SO.sub.3, --(CH.sub.2).sub.3 --SO.sub.3, --CH.sub.2 --CH(CH.sub.3)--CH.sub.2 --SO.sub.3, --CH.sub.2 --CH(OH)--CH.sub.2 --SO.sub.3, --CH.sub.2 --CH(OH)--CH.sub.2 --S.sub.2 O.sub.3, --Z--COO-- with Z being a divalent, optionally substituted hydrocarbon group, --CO--Z--COO--, PO.sub.3, PO.sub.2, --CH.sub.2 ).sub.n --PO.sub.3, --CH.sub.2).sub.n --PO.sub.2, with n=1, 2, 3 or 4, and wherein

• M is a cation selected from the group consisting of alkali metal, alkaline earth metal, Mn, Fe, Co, Ni, Cu, Zn, Al, NH.sub.4,
• in an amount of 0.01 to 5% by weight, based on the weight of the polyether.