Abstract: A plurality of parallel layers of fibers are laid in two crossed directions on a disposable support mandrel, pins are temprorarily implanted in the mandrel (15) composed of foam material in regions of evolution of its shape and at points where it is desired to change the direction of the fiber, a continuous thread (33) is stretched out between the pins so as to form crossed superimposed layers, and a continuous fiber (50) is introduced by means of a needle (43) through the layers and forms successive open loops (53). The loops (53) are maintained by the elastic pressure exerted by the foam material and the gripping action of said layers. The fibers are impregnated with a binder and the binder is hardened and the mandrel is destroyed.