Reinforcing material comprising a unidirectional reinforcing web formed of a series of at least 3 twisted carbon reinforcing yarns, 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 reinforcing yarns 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 carbon reinforcing yarn having an S-twist and at least one carbon reinforcing yarn having a Z-twist, and, with: - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is even, the number of twisted carbon reinforcing S-twist yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ which are each independently an integer within the range {[(total number of yarns)/4] - 35%; [(total number of yarns)/4] + 35%}, each endpoint of the range being rounded to the nearest integer if the formula defining it does not result in an integer, the other twisted carbon reinforcing yarns being Z-twist yarns; - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is odd, the number of twisted carbon reinforcing S-twist yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ, which are either two integers or two and a half integers, and are each independently within the range {[(total number of yarns)/4] - 35%; [(total number of yarns)/4] + 35%}, each endpoint of the range being rounded to the nearest integer or integer and a half if the formula defining it does not result in an integer or integer and a half, the other twisted carbon reinforcing yarns being Z-twist yarns; the plane Δ being the plane parallel to the general direction of extension of the unidirectional web and which divides said unidirectional web into two equal parts, being perpendicular to its surface. - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is even, the number of twisted carbon reinforcing S-twist yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ which are each independently an integer within the range {[(total number of yarns)/4] - 35%; [(total number of yarns)/4] + 35%}, each endpoint of the range being rounded to the nearest integer if the formula defining it does not result in an integer, the other twisted carbon reinforcing yarns being Z-twist yarns; - when the total number of twisted carbon reinforcing yarns forming the unidirectional reinforcing web is odd, the number of twisted carbon reinforcing S-twist yarns on one side of the plane Δ and the number of twisted carbon reinforcing S-twist yarns on the other side of the plane Δ, which are either two integers or two and a half integers, and are each independently within the range {[(total number of yarns)/4] - 35%; [(total number of yarns)/4] + 35%}, each endpoint of the range being rounded to the nearest integer or integer and a half if the formula defining it does not result in an integer or integer and a half, the other twisted carbon reinforcing yarns being Z-twist yarns;