A hair-cosmetic composition comprising, in a cosmetically acceptable medium, at least one film-forming gradient copolymer comprising at least two different monomeric residues, and displaying a mass polydispersity index (Ip) less than or equal to 2.5, wherein the composition is able to form a film that has a strain at break εr ranging from 5% to 2500%, and/or a Young's modulus ranging from 0.5 to 1200 Mpa, and/or an instantaneous elastic recovery εi greater than or equal to 10%. An aerosol composition packaged in an aerosol device, comprising a propellant and a haircare composition as defined above, and also a method for treating the hair, such as a styling method, comprising applying the haircare composition or the aerosol composition above to the hair.