Composition comprising, by weight, the total being 100 %: 50 to 100 % of at least one polyamide A1 of formula X.Y/Z or 6.Y2/Z in which: X denotes the residues of an aliphatic diamine having from 6 to 10 carbon atoms, Y denotes the residues of an aliphatic dicarboxylic acid having from 10 to 14 carbon atoms, Y2 denotes the residues of an aliphatic dicarboxylic acid having from 15 to 20 carbon atoms and Z denotes at least one unit chosen from the residues of a lactam, the residues of an a,-aminocarboxylic acid, the unit X1, Y1 in which X1 denotes the residues of an aliphatic diamine and Y1 denotes the residues of an aliphatic dicarboxylic acid, the weight ratios Z/(X+Y+Z) and Z/(6+Y2+Z) being between 0 and 15 %; 0 to 40 % of a plasticizer; 0 to 50 % of an impact modifier; and 0 to 50 % of apolyamide A2. The invention also relates to structures comprising a layer consisting of the above composition. This structure is useful for making devices for storing or transferring fluids, in particular in motor vehicles and heavy goods vehicles. The fluids may for example be petrol, diesel, hydraulic brake fluid, compressed air for the brake circuits of heavy goods vehicles, and hydraulic clutch fluid. The invention also relates to these devices. Such devices may be tanks, hoses, pipes or containers. These structures may include other layers consisting of other materials.