The invention relates to a composition, and structures having a layer made of said composition, in which the composition is, 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 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.