Tempered Glass. Tempered glass cools quicker than most other types of glass, and that makes it stronger. It's made by reheating basic annealed glass and then cooling it rapidly. This is called air quenching and makes the glass about four times stronger than annealed glass of the same size and thickness. Tempered glass has more tensile strength—meaning it can bend easier without breaking. It's often used in big windows or skyscrapers, since it's more wind resistant.