The present invention relates to crosslinked, water-soluble or water-dispersible polyurethanes of A) at least one water-soluble or water-dispersible polyurethane prepolymer having terminal isocyanate groups of a) at least one compound having a molecular weight in the range from 56 to 300 which contains two active hydrogen atoms per molecule, b) at least one polymer containing two active hydrogen atoms per molecule, c) at least one compound which contains two active hydrogen atoms and at least one ionogenic or ionic group per molecule, d) at least one diisocyanate, B) at least one polymer containing groups which are reactive toward isocyanate groups, chosen from hydroxyl, and primary and secondary amino and/or carboxyl groups, or the salts thereof.