The Type of Glass
All of the windows and windshields in your car are made from safety glass. That said, there is a difference between the safety glass in your front windshield and the glass that is used in the rest of your car. Windshields are made from laminated glass. Essentially, this is two or more layers of glass with a piece of clear vinyl in between the layers. This prevents the windshield from shattering into a bunch of sharp pieces that can then injure the vehicle’s occupants.
With the rear windshield, you have tempered glass. This is still a type of safety glass, but it performs differently. Glass is tempered by heating it to extreme temperatures and then letting it cool rapidly. This increases the strength of the glass considerably. Furthermore, it changes the way the glass breaks when it does shatter. Instead of breaking into large shards, it breaks up into small, pebble-like pieces.
Another issue is the features built in with the glass. Most rear windshields connect in with a defrosting grid to melt things like snow and ice when they build up on the windshield. This means that replacing a rear windshield is not as simple as seating the new glass. It has to be connected with the defrosting grid, and this adds time to the process.
As I mentioned in the section about the different types of glass, they break differently. A front windshield can shatter, but the laminated design usually keeps all of the shards intact. This makes it much easier to remove and clean up after a shattered front windshield. When a rear windshield shatters, it breaks up into thousands of tiny pieces. Before the new rear windshield can be installed, the vehicle needs to be cleaned. This is a simple enough task, but it adds a significant amount of time to the process of replacing a rear windshield.
If your rear windshield is broken, you should get it fixed right away. Beyond the issues with visibility, it is important to realize that the rear windshield plays a role in the structural integrity in many vehicle designs. If it is compromised in some way, it can’t serve this role as well as it should. Even if the damage appears to be minor, you should have the rear windshield inspected by a professional as soon as possible.