A cosmetic product for changing the natural colour of keratinous fibres comprising: at least one package comprising at least on multilayer film which comprises at least one first polymer layer, at least one second polymer later and at least one barrier layer； a cosmetic composition contained in the package comprising at least one oxidizing compound, which is a solid oxidising agent, and at least one thickening agent； and a colour composition contained in the package. The barrier layer may comprise a metal, preferably aluminium. The solid oxidising agent may be a percarbonate salt, perborate salt and/or a percarbamate salt. The thickening agent may be a polysaccharide, preferably a mixture formed from a cellulose gum, a hydroxyethylcellulose and a xanthan gum. The first polymer layer may be formed from polypropylene, polyethylene, polyester, polyamide or polyvinyl alcohol and the second polymer layer may be formed from polyethylene terephthalate or polyethylene naphthalate. A method for lightening or colouring keratinous fibres wherein the contents of the cosmetic product are mixed with water, applied to the fibres and subsequently washed off.
