MACOR machineable glass ceramic has a continuous use temperature of 800C and a peak temperature of 1000C. Its coefficient of thermal expansion readily matches most metals and sealing glasses. MACOR is non-wetting, exhibits zero porosity, and unlike ductile materials, won't deform. It is an excellent insulator at high voltages, various frequencies and high temperatures. When properly baked out, it won't outgas in vacuum environments.