Insulating materials in resistor manufacture In addition to the insulation requirements, insulating materials in resistor manufacture also have to be resistant against high temperatures. The most common insulating materials are ceramic materials like high-temperature ceramic compounds made from porcelain, alumina through to steatite, cordierite and high-grade aluminum oxide with a large variety of mechanical properties. They all share the following characteristics: a high application temperature and creepage resistance, a high insulation resistance and low water intake capacity combined with a high resistance to ageing. Unfortunately, they are highly susceptible to rupture and in most cases it is virtually impossible to process and deform the ceramic material after baking. Other materials used are silicates like glass or vitreous compounds and mica. Formerly, materials like marble, slate and asbestos were also used. Plastics are suited for applications where the operating temperatures are not too high (silicone rubber up to 250°C) or when it is guaranteed that inadmissibly high temperatures will not occur.