The use of a mixture of solid and hollow glass reinforcements with an alloy of at least one polyamide and at least one polyolefin, the mixture of solid and hollow glass reinforcements including from 5 to 50% by weight of hollow glass beads relative to the total of solid and hollow glass reinforcements for the dry preparation at 23° C. of a composition having a modulus at least equal to 8 GPa and a dielectric constant Dk less than or equal to 3.5 as measured according to ASTM D-2520-13, at a frequency of at least 1 GHz, at 23° C., under 50% RH.