Flexible semicrystalline polyamides

Multilayer structure in which the inner layer is in contact with petrol or diesel fuel and comprising, in succession from the outside inwards:

• an outer layer consisting of the 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:
• “6” denotes the residues of hexamethylene diamine,
• 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 α,Ω-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 a polyamide A2,
• a PA-6 layer or a layer of a PA-6/polyolefin blend having a PA-6 matrix and optionally containing a conductor.