Mica is an inorganic mineral. It is one of the best natural insulating materials available. In spite of the tremendous progress made in insulation technology this material and its product still find many applications in the present day. The qualities of mica can be classified on visual basic such as clear, stained spotted, etc. Mica sheets are used for the insulating leaves between commentator segments. These are however not obtainable in large thickness. Thus for commentator of considerable dimensions mica has been developed. This is achieved by sticking mica splitting on sheets of paper by means of a drying varnish such as shellac. These sheets are pressed between steam heated plates and then cooled. Mica is used for slot linings of have machines and for making bushes. Mica is usually avoided for slot linings of machines because its space factor is low. This means that adequate dielectric strength may be obtained with thinner layers of cotton tape and like materials than of mica.