Abstract: The reinforcing material comprises a unidirectional reinforcing web (2) formed of one or a plurality of carbon yarns (3), associated on at least one of its faces, preferably on each of its faces, with a porous polymeric layer (4, 5), the polymeric portion of the reinforcing material representing from 0.5% to 10% of its total weight and preferably from 2% to 6% of its total weight, characterized in that said carbon yarns (3) are individually twisted having a twist from 3 turns/m to 15 turns/m, preferably from 6 turns/m to 12 turns/m, and comprise at least one S-twist yarn and at least one Z-twist yarn, from a selection according to claim 1.