Composition comprising at least: a) a polyamide of type 6 or 66 obtained by means of a process of polymerization of the monomers of the polyamide 6 or 66 in the presence of monofunctional and/or difunctional compounds comprising carboxylic acid or amine functions; said polyamide having a melt flow index of greater than or equal to 10 g/10 min. according to the ISO1133 standard measured at a temperature of 275°C with a load of 325 g and a molecular weight Mn of between 3000 and 25 000 g/mol; said polyamide of type 6 being a polyamide comprising at least 90 mol% of caprolactam monomer residues; said polyamide of type 66 being a polyamide comprising at least 90 mol% of adipic acid and hexamethylenediamine monomer residues; said monomers of the polyamide 66 being adipic acid and hexamethylenediamine, or hexamethylenediamine adipate, also called Nylon salt or N salt; said monomers of the polyamide 6 being caprolactam or derivatives thereof; and b) an impact modifier comprising functional groups that react with the polyamide a), chosen from the group comprising ethylene/acrylic ester/glycidyl methacrylate terpolymers, ethylene/butyl ester acrylate copolymers, ethylene/n-butyl acrylate/glycidyl methacrylate copolymers, ethylene/maleic anhydride copolymers, maleic anhydride-grafted styrene/maleimide copolymers, copolymers of styrene/ethylene/butylene/styrene modified with maleic anhydride, maleic anhydride-grafted styrene/acrylonitrile copolymers, maleic anhydride-grafted acrylonitrile/butadiene/styrene copolymers, and hydrogenated versions thereof, the proportion of impact modifiers in the composition being between 0.1°7o and 10% by weight. a) a polyamide of type 6 or 66 obtained by means of a process of polymerization of the monomers of the polyamide 6 or 66 in the presence of monofunctional and/or difunctional compounds comprising carboxylic acid or amine functions; said polyamide having a melt flow index of greater than or equal to 10 g/10 min. according to the ISO1133 standard measured at a temperature of 275°C with a load of 325 g and a molecular weight Mn of between 3000 and 25 000 g/mol; said polyamide of type 6 being a polyamide comprising at least 90 mol% of caprolactam monomer residues; said polyamide of type 66 being a polyamide comprising at least 90 mol% of adipic acid and hexamethylenediamine monomer residues; said monomers of the polyamide 66 being adipic acid and hexamethylenediamine, or hexamethylenediamine adipate, also called Nylon salt or N salt; said monomers of the polyamide 6 being caprolactam or derivatives thereof; and b) an impact modifier comprising functional groups that react with the polyamide a), chosen from the group comprising ethylene/acrylic ester/glycidyl methacrylate terpolymers, ethylene/butyl ester acrylate copolymers, ethylene/n-butyl acrylate/glycidyl methacrylate copolymers, ethylene/maleic anhydride copolymers, maleic anhydride-grafted styrene/maleimide copolymers, copolymers of styrene/ethylene/butylene/styrene modified with maleic anhydride, maleic anhydride-grafted styrene/acrylonitrile copolymers, maleic anhydride-grafted acrylonitrile/butadiene/styrene copolymers, and hydrogenated versions thereof, the proportion of impact modifiers in the composition being between 0.1°7o and 10% by weight.