The invention describes cationically modified particulate anionic polyurethanes having a particle size from 10 nm to 10 μm, the particulate polyurethanes being cationically modified through surface coating with cationic polymers. Preferred cationic polymers are polymers containing vinylamine units, polymers containing vinylimidazole units, polymers containing quaternary vinylimidazole units, condensates of imidazole and epichlorohydrin, crosslinked polyamidoamines, ethyleneimine-grafted crosslinked polyamidoamines, polyethyleneimines, alkoxylated polyethyleneimines, crosslinked polyethyleneimines, amidated polyethyleneimines, alkylated polyethyleneimines, polyamines, amine-epichlorohydrin polycondensates, alkoxylated polyamines, polyallylamines, polydimethyldiallylammonium chlorides, polymers containing basic (meth)acrylamide or (meth)acrylic ester units, polymers containing basic quaternary (meth)acrylamide or (meth)acrylic ester units, and/or lysine condensates.