Tempered glass is made by heating flat glass to approach its softening temperature and suddenly chilling with jets of cold air, which distributes compression stress on the glass surfaces while tensile stress in the center. The counteraction of compression stress and tensile stress provides tempered glass times strength than normal glass. When broken, tempered glass forms oblique bean size granules to reduce damage to human bodies. Tempered glass also withstands quick temperature changes. Tempered glass mainly are used in auto side window glass, rear window glass.