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 formed from a polyamide or else a polyamide / polyolefin blend having a polyamide matrix ; b ) optionally , a tie layer ; c ) a layer 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 having a functional group capable of reacting with a polyamide having an amine end group ; the residues of the unsaturated monomer are attached to the backbone by grafting or copolymerization via its double bond ; the layers , and 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 .