Abstract: Films based on copolymers, their applications in transdermal systems and their processes of preparation. The said films consist of a hydrophobic polymer of ethylene/vinyl acetate (EVA) type containing at least one active principle and composed of 15 to 50% of hydrophilic inclusions formed from at least one hydrophilic monomer chosen from the group which comprises acrylamide, methylolacrylamide, diacetone acrylamide, maleic acid, acrylic acid, fumaric acid, itaconic acid, propylene glycol acrylate, ethylene glycol methacrylate, methacrylamide, methacrylic acid, propylene glycol methacrylate, hydroxyethyl methacrylate, dimethylaminoethyl methacrylate, N-vinylpyrrolidone, vinylacetic acid or vinylsulphonic acids.