[en] Object: To provide packing or lining materials or vibration resisting materials, possessing superior characteristics of both elasticity and corrosion resistance against UF₆, made from ethylene-hexafluoropropylene copolymers. Method: Ethylene-hexafluoropropylene copolymers, containing hexafluoropropylene by 10 - 50 mol %, are prepared by means of various methods. The copolymer is cross-linked in the form of powder or sheet or after it has been moulded into appropriate product forms. Crosslinking is achieved by either heating the raw copolymer mixed with t-butylperoxybenzoate by 3 to 100 at about 150⁰C, or irradiating with ionizing radiation, i.e., an electron beam by 12 Mrad under air-free atmosphere. The obtained cross-linked copolymer shows strong resistance against UF₆ gas even at 100⁰C and keeps high mechanical strength