Our polymer insulators material: 1.The core is the indoor insulating part of the insulators used to guarantee the mechanical charging placed on the lines. It is done of fibreglass laid in a resin matrix, in such a way to get the maximal holding to the traction.The core is circular. 2.The covering (sheds)is the insulating outdoor part of the insulator, it is made of silicon rubber, it serves to insure the necessary creepage and it saves the core from bad weather. 3.The metallic endings of the insulators done of steel mould and warmly galvanized. We are a leading manufacturer and exporter of various kinds of lightning arrester(Metal oxide),composite insulator,fall-type fuse and isolation knife,over-voltage protector,resistance slice,Discharging counter etc For the details please consult our website If you are interested in our products, please do not hesitate to contact us. Thanks!