Tempered glass is up to five times stronger than standard glass. Historically, two different methods for strengthening glass have been used – chemically strengthened glass and tempered glass.
Tempered glass is made by first heating the glass in an oven at around 700°C and then quickly cooling it with compressed air. The tempering process leaves the glass with a difference in inner and outer tension that makes it break up into granules rather than splintering when broken.
Chemically strengthened glass is made by lowering sheets of glass into a potassium salt solution at a temperature around 400°C. During this process, tension builds on the surface of the glass giving it the added strength.