The present invention relates to a process for treating keratin fibers comprising the steps of: applying onto the keratin fibers a composition comprising at least one cationic polymer then placing the keratin fibers in an occlusive space and then heating the keratin fibers, wherein the composition contains neither a reducing agent nor a source of carbonate ions of the formula: wherein X is a group selected from the group consisting of O-, OH, NH2, O-OH, and O-COO-. The present invention also relates to the composition itself and a kit to be used for the above process.
