25kV pin type insulator in China are made by the wet process using high grade raw materials. The basic raw materials that go into the manufacture of these insulators which are naturally occurring clays and minerals like quartz and feldspar.

The coarsely-powdered materials are ground to the required particle size in ball mills. The moisture content is reduced in filter process to obtain solid cakes. The cakes are fed into the pug mills. The void free pugs that are extruded from the pug mills are then pressed into shape and glazed after drying. These insulators which are thoroughly inspected before glazing are fired in the tunnel kilns.