A magnetically loaded composite rotor is formed by providing a mandrel 1 having a longitudinal axis 2. A release agent 3 is coated on the mandrel and a fiber material 4 of woven or non-woven material having fibers extending in the direction of the axis 2 is applied over the release agent. A thermoplastic resin impregnated tow 24 including magnetic particles 28 is wound over the fiber material 4, the fiber material substantially preventing the magnetic particles penetrating through to the mandrel.