The general field of the invention is that of helmet shells made of composite material comprising at least one “armure” of fabrics impregnated with a resin matrix. Certain parts of the “armure” are impregnated with a resin matrix comprising an additive adapted to reinforce the mechanical strength of the helmet, the said parts corresponding to the weakest zones of a human head, such as the top of the head or the ears. Preferably, the resin is of the epoxy type and the additive is based on acrylic block copolymers. More precisely, the additive is of the “Nanostrength®” brand.