Toughened glass or tempered glass is glass that has undergone processes of controlled thermal treatment to increase its strength. It is four times stronger than normal annealed glass. Toughened glass is made from annealed glass that has been heated to approximately 650⁰C and then rapidly cooled. Due to the increased heat treatment and rapid cooling of the glass, the treatment produces different physical properties. This results in compressive stress on the surface and improved bending strength of glass. Before toughening, the glass must be cut to size or pressed to shape.
Toughening does not alter the basic characteristics of glass-like light transmission and solar radiant heat properties of normal glass. It can neither be cut nor altered. Toughened glass is known to have higher thermal strength, with the ability to withstand high-temperature changes up to 250°C. A safety glass, toughened glass is difficult to break but in the event of a breakage, disintegrates into small globules.