Abstract: A mandrel is provided for use on a filament winding machine in a process for making a fibre-reinforced plastic artifact. The mandrel 50 comprises a portion 66 of relatively low density cellular material such as foamed polyurethane about a stiff axial spine member 54. The mandrel 50 is therefore relatively light weight and yet is of sufficient rigidity for use on a filament winding machine. After formation of an artifact by winding on the mandrel 50, the mandrel 50 may be removed from inside the artifact by comminution.An alternative mandrel comprises a number of sections of the cellular material, and enables an artifact having a re-entrant surface to be formed by a filament winding process. A layer of resin-impregnated filaments is wound around the mandrel, and the layer is partially cured. A section of the mandrel is then removed by comminution, and the layer is deformed to the shape of the remainder of the mandrel.