A process for treating keratin fibres may include applying a hair treatment composition to the keratin fibres. The composition may comprise at least one of fatty substances, surfactants, polymers with a glass transition temperature (Tg) ranging from about 40° C. to about 150° C., oxidation dye precursors, and direct dyes. The process may also include inserting the keratin fibres into a device comprising two elements that are moveable relative to each other between an open position and a closed position. In the closed position, the two elements may define a substantially leaktight closed space. The process may further include moving the two elements into the closed position to confine the keratin fibres in the closed space, and heating the keratin fibres to a temperature ranging from about 40° C. to about 250° C. while the keratin fibres are confined in the closed space.
