Toughened glass is also known as "Secure Glass" or "Safe Glass". Toughened glass is 4 to 5 times stronger than annealed glass of the same type and thickness. It is due to stresses in the surface layer. The compressive surface stresses close microscopic crack and make the glass much stronger. The toughened glass is 2-3 times more resistant to thermal shocks as an annealed glass. The annealed glass is a brittle material. It breaks under a lowest tensile stress. The tensile stresses on the surface can be caused by bending the glass sheet or by changes in temperature. The normal glass can break at 40 – 50 o C, but the tempered glass remains unbreakable even at 150 o C. When ordinary glass is broken, it forms sharp, knife like pieces, but the toughened glass breaks into small harmless pieces. Toughened glasses have a wide range of applications.