The invention provides a pipe having a pipe wall comprising a polyolefin layer 21, and bonded thereto with no intervening adhesive layer a barrier layer 22 formed of a barrier material, which barrier material has enhanced resistance to the permeation therethrough of gaseous and/or hydrocarbon materials relative to the polyolefin; either the polyolefin layer or barrier layer or both having adhesive polymer units incorporated therein, in at least the region of an interface between the layers; the adhesive polymer units being present in a concentration effective to bond the polyolefin layer 21 to the barrier layer 22. In a preferred embodiment, the adhesive polymer units are contained within the barrier layer, which is preferably formed of a rubber-modified polyamide.