There are several types of safety glass. Tempered glass is basically stronger than regular glass, and when it breaks it shatters into little pieces. The preferred glass for shower doors, laminated glass, takes a different approach to meeting the safety standards. This glass is usually two pieces of normal glass laminated together with a gummy jell, or PVB. This is the safety glass used in car windshields. There is also Wire Glass which was used in showers for a short time before tempered glass became prevalent. It is still used as a type of safely glass where there are fire codes involved.

        Pilkington Safety Glass.pdf