Prepregs are known as sheet materials made of toughened fibers (reinforced fibers, carbon fibers, etc.) impregnated with an uncured thermosetting resin. In the field of golf club shafts, a plurality of prepregs are wound on a mandrel that has the shape of a tapered shaft and are thermally cured into a tapered golf club shaft.
FIG. 10 shows a typical example of a structure of a golf club shaft 1 that is configured from a plurality of prepregs. The golf club shaft 1 includes a compressive rigidity (crush rigidity) holding layer 2, a torsional rigidity holding layer 3 and a bending rigidity holding layer 4, in that order from the under layer, wherein the compressive rigidity holding layer 2 is configured from a prepreg (90-degree (hoop) layer prepreg) whose fiber direction is orthogonal to the longitudinal direction of the shaft, wherein the torsional rigidity holding layer 3 is configured from a prepreg (bias prepreg; prepreg of a 45-degree layer) whose fiber direction is inclined to the longitudinal direction of the shaft, and wherein the bending rigidity holding layer 4 is configured from a prepreg (prepreg of a 0-degree layer) whose fiber direction is parallel to the longitudinal direction of the shaft. The compressive rigidity holding layer 2 is sometimes layered on top of the torsional rigidity holding layer 3. The prepregs configuring the compressive rigidity holding layer 2 and the bending rigidity holding layer 4 are each usually referred to as an UD (unidirectional) prepreg since the fibers thereof extend in a single direction. In addition, the torsional rigidity holding layer 3 usually includes a pair of UD prepregs (45-degree layers/bias prepregs) whose fiber directions are symmetrical with respect to the longitudinal direction of the shaft (generally ±45° relative to the longitudinal direction); in addition, the applicant has also developed the golf club shaft 1 in which a plain weave fabric (biaxial woven fabric) prepreg, a triaxial woven fabric prepreg and a tetra-axial woven fabric prepreg that are made by impregnating a plain weave fabric (biaxial woven fabric), a triaxial woven fabric and a tetra-axial woven fabric with thermosetting resin are incorporated in the torsional rigidity holding layer 3.