In the production of flat glass the molten silica-based mix is cooled slowly under carefully controlled conditions. This annealing procedure removes undesirable stresses from the glass. Cooling occurs in an annealing "lehr"; Hence, the glass is termed "annealed" or "ordinary" glass. Annealed glass which has been heated to a temperature near its softening point and forced to cool rapidly under carefully controlled conditions is described as "heat-treated glass. " The heat treating process produces highly desirable conditions of induced stress which result in additional strength, resistance to thermal stress, and impact resistance.

Tempered glass used widely for furnitures and building.