The difference between windshield glass and the other glass in a vehicle, including the rear window, is that the windshield is made from laminated glass whereas the side and rear windows are made from tempered glass. Laminated glass is constructed from two panes of glass, which has a thin layer of transparent vinyl in between them.
For the windshield, the two pieces of glass and the vinyl are laminated together using heat and pressure in an autoclave. Laminated auto glass provides the highest levels of safety in a crash, as the glass may shatter, but it usually does not fly apart because the broken pieces of glass adhere to the vinyl layer. When an object strikes the windshield, it is usually only the outer layer of glass that cracks or breaks.
The rear and side windows of a vehicle use glass that is tempered by heating it to more than 1,100 degrees Fahrenheit and then cooling it quickly. This tempering process produces glass that is much stronger than untempered glass of the same thickness. When tempered glass is broken, it breaks apart into tiny pieces, which ensures that there are no large or jagged pieces that could injure the driver or passengers.
All glass used in an automobile must conform to the Federal Motor Vehicle Safety Standards.