The present invention relates to a process for treating keratin fibers such as the hair using a packaging article comprising i) an envelope defining at least one cavity, the envelope comprising water-soluble and/or liposoluble fibres, preferably water-soluble fibres； ii) at least one anhydrous oxidizing composition, preferably in paste or powder form, comprising at least one anhydrous chemical oxidizing agent, preferably in paste or powder form； it being understood that the oxidizing composition is in one of the cavities defined by the envelope i).
