(EN) The invention relates to a crosslinked polyurethane comprising
A) at least one polytetrahydrofuran of the formula ![embedded image]()
B) at least one compound which contains more than 2 active hydrogen atoms per molecule C) at least one compound which contains at least 2 active hydrogen atoms per molecule and at least one ionogenic and/or ionic group per molecule, where the groups may be anionogenic, anionic, cationogenic or cationic D) at least one diisocyanate E) optionally a compound different from B) and C) which contains at least 2 active hydrogen atoms and has a molecular weight of from 60 to 5000 or the salts thereof.