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