They are made of special ceramic material that has the properties of low expansion and high strength under 1300C high temperature. Moreover, our series products are of the excellent resistance to sudden cold or heat(from 400C to 20C quickly  cold, they will not be destroyed) and to acid and alkali and not contained toxic, lead and other chromium dissolved substance, which can preserves the heat and orginal flavor and taste of food exceptionally well. So it is looked on as one of the best green environment-protection products.