The present invention relates to a process for grafting an unsaturated monomer onto a fluoropolymer, having the steps of: a) melt blending the fluoropolymer with the unsaturated monomer; b) forming the blend obtained in a) into films, sheets, granules or powder; c) exposing the products from step b), in the absence of air, to photon (y) or electron (β) irradiation with a dose of between 1 and 15 Mrad; and d) optionally treating the product obtained at c) in order to remove all or part of the unsaturated monomer that has not been grafted onto the fluoropolymer. Structures made with these materials are barriers to many fluids and in particular to petrol and to air-conditioning fluids and may be formed into bottles, tanks, containers, pipes, hoses and vessels of all sorts. They may also be converted into films with which packaging is made.