A cosmetic agent for lightening keratin fibers, containing at least one packaged preparation (A), wherein preparation (A), based on its total weight, contains about 10-90% by weight of peroxydisulfate(s), from about 10-50% by weight of sodium silicate and preparation (A) is packaged in a water-soluble film which, based on its total weight, consists of at least 60% by weight of a polymer mixture which has a multi-modal molecular weight distribution. The sodium silicate may comprise sodium disilicate. The polymer mixture may comprise at least 60% by weight of a mixture comprising water-soluble vinyl alcohol / vinyl acetate copolymer a1) and at least one water-soluble vinyl alcohol / vinyl acetate copolymer a2) which is different from a1). The polymer mixture may comprise at least 60% by weight of a mixture comprising water-soluble vinyl alcohol / vinyl acetate copolymer a1) and at least one optionally modified water-soluble polysaccharide from the group consisting of methylcellulose, carboxymethylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, dextrin and hydroxypropylstarch. The cosmetic agent may further comprise a flowable preparation (B) which, based on its weight comprises 50-98% water and 0.5-20% hydrogen peroxide. A method for the colour change of keratin fibres in which preparation (A) is introduced into preparation (B) by dissolving the water-soluble film.
