Schott Nextrema glass ceramic sheet. It is available in a range of colours, including transparent, translucent white, opaque white, tinted, translucent blue-grey and opaque grey. Due to its robustness at very high temperatures, thermal shock resistance and impermeability to gases, it is used in a range of demanding industrial as well as domestic applications, for things like heating a lighting (sauna, IR-heating), cooking appliances (toasters, grills, microwave), and cover panels (such as for heating elements). Image Schott.