The rear windshield glass is tempered to increase protection for people in the vehicle. Tempering the glass makes it about five to 10 times stronger than normal glass, meaning it can withstand impact and extreme temperatures.
Tempered
The process of tempering reheats the glass to a temperature where it reaches a near-liquid state. The glass is then cooled and compresses, increasing its strength against impact.
Compression
In order to shatter tempered glass, the impact would have to overcome the compression of the glass. When tempered glass is broken, the breakage pattern, also known as dicing, results in tiny pieces of glass rather than large shards, which could do considerably more damage to the individuals within the car.
Causes
Some common causes of glass shatter includes acts of vandalism, when the windshield is smashed with blunt objects such as a baseball bat; rocks or other debris kicked up by other vehicles, especially on highways; and fallen tree branches.
