PURPOSE: To make an insulator thin and improve its radiation resistance by applying and baking polymide varnish onto an ETFE resin insulator.

CONSTITUTION: As an insulator for wires and cables, an ETFE resin 2 having excellent heat resistance and mechanical properties as well as comparatively excellent radiation resistant is used. Furthermore, as a jacket layer, a polymide varnish application and baked layer 3 having excellent heat resistance and radiation resistance 5μm or greater in surface layer thickness, is provided. The reason why the polymide surface layer thickness is made 5μm or greater is that the strength of the surface layer is kept at least at about 10kg/mm2 and a surface layer free from pin holes are formed, preferably in the range of 5 to 50μm. An cross-linking agent such as tryallylsianulate should preferably be combined in ETFE resin, resulting in a decrease in the amount of the deformation due to heating. In that instance, the combine ratio is 1 to 20wt.%. As a result of this, an insulator can be made thin and wires and cables having excellent radiation resistance for a long period of time can be obtained.