A process for the treatment of non-keratinaceous textiles, preferably cellulosic fibers, which comprises the step of treating the textiles with a composition which comprises: a self-crosslinking polymer and a nucleophilic species (preferably a polymer comprising at least one protected thiol group), and a textile compatible carrier. Under domestic washing conditions the polymer forms reactive thiol groups which are capable of causing covalent cross-linking with the polymer. Preferably, the thiol group is protected as an isothiouronium group.