Saint Gobain-Glass Toughened Toughened or tempered glass is glass that has undergone processes of controlled thermal treatment to increase its strength. 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, especially between the surface and the inside 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. This is because once it is toughened, it cannot be re-worked on. Toughened glass is widely used in a number of applications.