The strength and safety properties of tempered glass is achieved by heating annealed glass in a tempering oven between 1100 – 1150 degrees F. The glass surface is then rapidly cooled with high-pressure blasts of air, causing the outer surfaces of the glass to cool and contract faster than the center. As a result, the surfaces of the glass are in compression while the core is in tension to balance it giving the glass its strength.
This process also gives tempered glass a distinct break pattern. Annealed glass breaks easily and fractures into large, sharp pieces that can inflict significant harm or injury. In contrast, because tempered glass is ten times stronger, it fractures into relatively small pieces when broken. This significantly reduces the chances of injuries or harm.