A composition including: between 45 and 94.95 wt. % of a matrix having at least one polyamide; between 0.05 and 20 wt. % of at least one prepolymer, the proportion by weight of the polyamide matrix and that of the prepolymer being respectively between 60 and 99.9 wt. % and between 40 and 0.1 wt. % in relation to the total amount of polyamide-prepolymer; between 5 and 45 wt. % of at least one impact modifier; and between 0 and 20% of an additive, said composition having a higher level of fluidity in the melted state than the same composition without prepolymer.