A two-part cosmetic product for sequential application to hair fibers of the scalp, eyebrows or eyelashes to impart a swelling effect comprising an anhydrous base coat composition and a water containing polymer as top coat, wherein a) the anhydrous base coat composition comprises at least one water absorbent compound which is a cosmetically acceptable salt of acrylic or polyacrylic acid, a CO 2 releasing compound which is an inorganic or organic carbonate, or bicarbonate, a solvent for the water absorbent compound and the CO 2 releasing compound, a wax and auxiliary substances which do not encompass surfactants, wherein the solvent is a silicone compound which does not allow an interaction of the salt of acrylic or polyacrylic acid and CO 2 releasing compound before the water containing polymer of the top coat is applied to the base coat composition and wherein the salt of acrylic or polyacrylic acid and the CO 2 releasing compound are contained in an amount effective to interact and generate CO 2 when the water containing polymer is applied, the amount of the salt of acrylic or polyacrylic acid being 15-35 % by weight and the amount of the CO 2 releasing compound being 10-80 % by weight, the weight being based on the total weight of the base coat composition and wherein b) the water containing polymer which is a film former selected from the group comprising a polyurethane, an acrylate copolymer, a methacrylate copolymer, an acrylamide, an acrylamide copolymer, PVP, PVP copolymer, chitosan, a chitosan copolymer, a polyquaternium, a water soluble polyester and mixtures of these film formers has a viscosity which is smaller than that of the base coat composition, and the polymer is present in the top coat in an amount from 25 to 35 weight %, based on the total weight of the water containing polymer, being effective to form a film on the hair fibers and to be expanded by CO 2 after application to the base coat composition. a) the anhydrous base coat composition comprises at least one water absorbent compound which is a cosmetically acceptable salt of acrylic or polyacrylic acid, a CO 2 releasing compound which is an inorganic or organic carbonate, or bicarbonate, a solvent for the water absorbent compound and the CO 2 releasing compound, a wax and auxiliary substances which do not encompass surfactants, wherein the solvent is a silicone compound which does not allow an interaction of the salt of acrylic or polyacrylic acid and CO 2 releasing compound before the water containing polymer of the top coat is applied to the base coat composition and wherein the salt of acrylic or polyacrylic acid and the CO 2 releasing compound are contained in an amount effective to interact and generate CO 2 when the water containing polymer is applied, the amount of the salt of acrylic or polyacrylic acid being 15-35 % by weight and the amount of the CO 2 releasing compound being 10-80 % by weight, the weight being based on the total weight of the base coat composition and wherein b) the water containing polymer which is a film former selected from the group comprising a polyurethane, an acrylate copolymer, a methacrylate copolymer, an acrylamide, an acrylamide copolymer, PVP, PVP copolymer, chitosan, a chitosan copolymer, a polyquaternium, a water soluble polyester and mixtures of these film formers has a viscosity which is smaller than that of the base coat composition, and the polymer is present in the top coat in an amount from 25 to 35 weight %, based on the total weight of the water containing polymer, being effective to form a film on the hair fibers and to be expanded by CO 2 after application to the base coat composition.