To obtain a silicone polymer insulator which is excellent in electrical properties (e.g. resistances to tracking and errosion) without detriment to the excellent characteristics inherent in a silicone rubber (e.g. high insulating proper ties, weatherbility, and water repellency) and which exhibits remarkable effect in preventing corona noise of flash over in a stained zone.

This insulator is the one at least the surface layer of which comprises a material formed by curing a silicone rubber compsn. The compsn, comprises 100 pts.wt organopolysiloxane reprented by the formula R1nSiO(4-n)/ 2 (wherein each R1 is independently an optionally substd. monovament hydrocarbon group; and (n) is 1.98-2.02), 0.05-20 pts.wt. hydrocarbon oil and/or fluorine oil exhibiting a voltage loss of 30% or lower after 4hr and 250°C in a nitrogen atmosphere, and a curative in an amt. enough to cure the organopolysiloxane. The polymer insulator is produced by forming a cured material layer from the compsm. on the surface of an insulator made from a material other than a silicone polymer.