Tempered glass is made of ordinary glass, heated to above 600 degrees, and then quickly cooled with air. The generated internal stress can greatly improve the strength and temperature mutation resistance of glass. When damaged by external force, due to this internal stress, the stress balance around the damage point will be destroyed, resulting in a chain reaction, leading to the whole glass breaking. Because this kind of stress imbalance can only be borne by small pieces of glass, the fragments are very small, so it will not cause serious harm to people (just cut the skin).

The windshield was tempered glass in the early days, and later it was changed to composite glass, that is, resin (usually PVB) was sandwiched between two layers of glass. The resin in the middle sticks the glass firmly like glue, even if it is broken, it will not fall off and will not fly around and hurt people. These two layers of glass are generally made of ordinary glass, but also tempered glass. The difference is that the windshield made of ordinary glass has low strength, but tiny cracks can be repaired, while the windshield made of tempered glass has high strength, but tiny damage will expand rapidly and cannot be repaired. Obviously, the former is more economical.