There are two main types of auto glass — tempered glass and laminated safety glass. Tempered glass, which typically is used on the rear and side windows, goes through a special process where it is heated and then quickly cooled. Laminated safety glass, which is typically used on windshields, is composed of two pieces of glass with a thin layer of vinyl. It’s then heated and pressed together in an oven called an autoclave. Both types of glass are stronger and more impact resistant than regular glass. When tempered glass receives a strong hit, it will shatter, but it will shatter and fall to the ground into small pieces that do not have sharp edges like regular glass. When laminated safety glass receives a strong impact it will also shatter but, generally, the pieces will adhere to the vinyl and not fall to the ground.
In automobile accidents auto glass is often damaged and needs to be replaced, but this isn’t the only instance where replacement is required. Gravel kicked up on the freeway can result in a chip or small vein in the windshield. Over time vibration, rain/snow, and temperture fluctuations can cause the vein to grow. In some states driving with damaged auto glass is a ticket-able offense. In Alaska, the DMV requires a non damaged windshield to take any driving test.