Abstract: Composition comprising a mixture from 20 to 70 parts by weight of polynorbornene, from 80 to 30 parts by weight of crystalline polyolefine and a quantity of plastifier for the polynorbornene sufficient to lower its glass transition temperature down to the range of rubbers, characterized in that, a copolymer of ethylene and at least one .alpha.-olefine having from 3 to 10 carbon atoms is used as crystalline polyolefine, said copolymer having a density between 0.89 and 0.93, a crystallinity ratio between 15 and 50% and a fluidity index between 0.5 and 15 dg/min. Such compositions are used to fabricate finished products and industrial articles by using the techniques of extrusion, injection moulding and compression moulding. Particular applications are flexible pipes, joints for the building and car industries, protection bellows for the car industry, injected articles.