Prepolymers and cellular polyisocyanate polyaddition products produced therefrom

prepolymer having an NCO content of less than 10%, based on the reaction of (A) diisocyanate with (b) polyether alcohol, wherein the (b) polyether alcohol contains (B1) and (b2) and / or (b3) with the following meanings for (b1), (B2) and (b3):(B1) polytetrahydrofuran having a molecular weight 1800-2100 g / mol and(B2) polyether alcohol a molecular weight from 500 to 7000 g / mol and based of Ethylonoxid and / or propylene and / or(B3) polytetrahydrofuran having a molecular weight between 800 and 1200 g / mol.