This specification applies to flexible cords insulated with polymeric compound (with and without glass fibre reinforcement) of the polytetrafluoroethylene (PTFE) type. The cords are intended for use at maximum operating temperatures of up to 200 degrees Celsius depending on the material of the conductor, insulation and sheathing (if any) and are for use in electrical installations at working voltages not exceeding 250 voltolts to earth or 440 volts between phases.