Synthetic resinous tube

A dimensionally stable tube having a plurality of layers of different polymeric materials cohesively bonded together, said tube having been made by the method comprising simultaneously coaxially extruding a plurality of contiguous tubular layers of different fuse bondable thermoplastic polymeric materials, at least one of the layers being susceptible to cross-linking by electron irradiation and at least one layer being substantially nonsusceptible to cross-linking by electron irradiation, and irradiating the resulting tube until cross-linking of the susceptible thermoplastic layer has progressed to a point where the said susceptible layer is substantially non-thermoplastic, wherein the at least one layer which is susceptible to cross-linking is an ethylene-propylene-diene terpolymer composition and the at least one layer which is substantially non-susceptible to cross-linking is a polyethylene composition.