The first car to offer a windshield as standard fare was a 1915 Oldsmobile. Until then, drivers could equip their Model T with a horizontally split piece of plate glass no different than the stuff in their home windows and swap it out when it got too dirty.
These days, modern technology has given us new types of glass that are curved and custom-made to perform in automotive applications. But just how does the glass in your car differ from run-of-the mill single-pane window glass?
The Two Types of Automotive Glass
If you’ve never seen the way a windshield looks after a serious impact, Google it — we’ll give you a moment. The way windshield glass absorbs impact is different than more common types of glass, because it is constructed as safety glass. This means two layers of glass are bonded to PVB to make the window, and the connective laminate between them provides structure in the case of an impact.
Your car’s windows are also made of a special type of glass, but it’s not the same as the safety glass in your windshield. Side windows are made of tempered glass, which has been hardened using advanced heating and cooling techniques.
Cool Feature or Safety Hazard?
What happens when new designs require automotive glass to be used in applications different from what we’ve seen in the past? For example, Tesla’s Model X SUV and even the older Model S use large panoramic glass roofs that might be forced to bear loads in the event of a rollover. Is such a design safe?
The answer is yes, so long as engineers adhere to the standards set forth by the Auto Glass Safety Council (AGSC) and National Highway Traffic Safety Administration (NHTSA). These are just two of the groups responsible for making sure new and replacement auto glass meets safety requirements.
In the Model X, and even in older cars such as Porsche’s 911 Targa with its panoramic glass roof, the concern is torsional rigidity. Basically, if the car rolls and there is a twisting force applied to the body, will the glass break? To reinforce the car’s metal body, engineers place braces and cross members at the front and rear of the glass. Sometimes cross members are even placed in the middle of a large pane.
The Future of Auto Glass
Thanks to its exceptional safety characteristics, as well as the improved insulation it provides, many manufacturers are considering the use of laminated auto glass in all of their cars. BMW has even started using the double-layered safety glass in small fixed side windows to deter theft, a byproduct of laminated glass being ten times as strong as tempered glass.
While this might seem like a no-brainer, there is a reason not to make use of the ultra-resilient windshield material everywhere. Sometimes people do in fact need to break the glass from the inside of the car. In such a case, the increased strength of a laminated glass window might even keep an occupant with a glass-breaking tactical pen — yes, that’s a thing — from making their escape.
Scott Huntington is a guest NMA blogger who is an automotive writer from central Pennsylvania. Check out his work at Off The Throttle or follow him on Twitter @SMHuntington.
