What type of car window glass shatters into small pebbles to reduce injury?

Tempered glass is the type of car window glass designed to shatter into small, relatively blunt pebbles to reduce injury. It is made by heating glass and then cooling its surfaces rapidly, creating compressive stress on the outside and tensile stress inside.

That treatment makes the pane several times stronger than ordinary annealed glass. When a severe impact finally breaks it, the stored stresses cause it to fragment into many small pieces rather than long, dagger-like shards. Side and rear vehicle windows commonly use this construction.

A common mix-up is the term “toughened glass,” which is a widely used synonym for tempered glass. “Safety glass” is broader: it can refer to tempered glass or laminated glass. Laminated glass, used chiefly for windshields, has plastic between glass layers and usually cracks while remaining together instead of exploding into loose fragments.