Abstract: The present invention relates to a multilayer structure based on polyamides and graft copolymers having polyamide blocks, comprising, in this order: a) a first layer (1) formed from a polyamide (A) or else a polyamide (A)/polyolefin (B) blend having a polyamide matrix; b) optionally, a tie layer (2a); c) a layer (2) based on a graft copolymer having polyamide blocks, formed from a polyolefin backbone and from at least one polyamide graft in which: the grafts are attached to the backbone by the residues of an unsaturated monomer (X) having a functional group capable of reacting with a polyamide having an amine end group; the residues of the unsaturated monomer (X) are attached to the backbone by grafting or copolymerization via its double bond; the layers (1), (2a) and (2) being successive and adhering to one another in their respective contact region. One particularly useful application relates to tubes for cooling circuits of internal combustion engines, such as the engines of cars or lorries.

Abstract: The present invention relates to a multilayer tube comprising, in its radial direction from the outside inwards: an outer layer (1) made of a polyamide chosen from PA-11, PA-12, aliphatic polyamides resulting from the condensation of an aliphatic diamine having from 6 to 12 carbon atoms and of an aliphatic diacide having from 9 to 12 carbon atoms, and 11/12 copolyamides having either more than 90% of 11 units or more than 90% of 12 units; a tie layer; a layer (2) made of a polyamide (A)/polyolefin (B) blend (2) having a polyamide matrix; a tie layer; an inner layer (3) made of a polyamide that is chosen from the same products as the outer layer and may be identical or different; the layers being successive and adhering to one another in their respective contact zones.