the present invention relates to a process for retanning chrome - tanned leather comprising applying to leather a reaction product of at least one glycerol monoester of a saturated c 12 - 18 monocarboxylic acid , at least one diisocyanate selected from the group consisting of toluene diisocyanate , hexamethylene diisocyanate , and isophorone diisocyanate , and dimethylolpropionic acid , wherein the components , and are so selected that the molar ratio of the isocyanate groups of component to the sum of the hydroxyl groups of components plus is about 0 . 5 to about 1 . 05 and the molar ratio of compound to compound is about 0 . 7 to about 1 . 5 and wherein the carboxyl groups originating from compound are at least partly neutralized .