An element of a line system of a fuel cell, in which the part which is in contact with the medium being conveyed comprises a polyamide molding composition and, in addition, at least one further layer selected from among: a) a layer II of a further polyamide molding composition; b) a layer III of a molding composition comprising a functionalized polyolefin; c) a layer IV of a polyolefin molding composition in which the polyolefin is not functionalized; and d) a layer V of an EVOH molding composition, is present, can be produced inexpensively and has a good barrier action against the medium being conveyed.