A jig (10) is used to form a coil (50) for an electrical machine. A plurality of conductive wires (56), each covered in a heat-curable electrically insulated material, are wound around a bobbin (12). Each succeeding winding in contra-wound relative to the previous winding, with the first turn (16) of each succeeding winding overlaying the last turn (5) of the previous winding. Undeformable electrically insulated inserts (54) are inserted into the windings before heating and compressing the coil (50) in the jig (10).