the present invention is directed to a process for the preparation of foam - containing polyurethane masses comprising reacting an isocyanate prepolymer containing cation groups with water in the presence of fillers . the isocyanate prepolymer is prepared by first i ) reacting a polyisocyanate with a first polyol which contains partly or completely quaternized tertiary nitrogen , said polyol being prepared by reacting a tertiary amine containing compound with from 3 to 8 moles of propylene oxide per mol of nitrogen to thereby form a semi - isocyanate prepolymer and then ii ) reacting said semi - isocyanate prepolymer with a second polyol different from said first polyol , to form said isocyanate prepolymer .