Copolymer of steareth-20-methacrylate and acrylic acid/methacrylic acid and their esters, cross-linked with pentaerythritol allyl ether Steareth-20-methacrylate is an ester of methacrylic acid with polyaethylene glycol (average 20 units -CH2-CH2-O-): The substance belongs to the group of film-forming substances and is used in cosmetic products for hair, skin and nails.