Toughened glass is strong, has enhanced thermal resistance, and breaks into small cuboid fragments rather than shards and is less likely to cause injury. The greater contraction of the inner layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass. This compressive stress on the surface of the glass is typically as high as 50 MPa. It is this compressive stress that gives the toughened glass an increased strength.

Uses

Toughened glass is used when strength, thermal resistance and safety are important considerations. The most commonly encountered tempered glass is that used for side and rear windows in automobiles, used for its characteristic of shattering into small cubes rather than large shards. Tempered glass is also used in buildings for unframed assemblies (such as frameless doors), structurally-loaded applications, and any other application that would become dangerous in the event of human impact.

Manufacturing

Toughened glass is made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it above its annealing point of about 720 °C. The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time.