Why is the glass in your car different from the glass in your house or even the glass holding your drink?
Laminated vs. Tempered
There are a few different components that dictate which type of glass goes where, and I’m here to answer any questions you may have or tell you some interesting information you may have not known otherwise.
The first windshield was invented in 1904 and began its long journey in Henry Ford’s Model T after wearing goggles to protect your eyes from debris became inconvenient. It consisted of two plate glass sheets, one on top of the other. This was designed so that if the first sheet of glass became dirty from dust and things, it could be “folded” down to reveal a clean windshield. But what if that one got dirty?
In 1916, Mary Anderson’s windshield wipers became commonplace. They were first operated with hand cranks inside the vehicle and made it so that a total windshield replacement wasn’t necessary every time the glass got rained on. Fast forward to 1934 when the first curved windshield was invented. This allowed for more visibility and structural integrity. Furthering that, in 1949 tempered glass became available for the sides and rear of the car as well as laminated glass for the windshield itself. Laminated safety glass is what is used today and in most countries, including the United States, is required by law.
Laminated safety glass is reserved for your windshield only. This is because it’s more durable than tempered glass, more expensive to make, and stronger structurally than tempered glass is. It’s composed of 3 layers; the inner layer is made of a plastic called polyvinyl butyral, or PVB. This plastic is squished between two layers of clear tempered glass. The PVB on the inside isn’t just for structural integrity, though it does add strength to the windshield; its main purpose is to keep the glass from shattering on impact.
Say you’re driving down a dirt road in Sedona, Arizona, and a huge rock is kicked up by the tires and hits your windshield square in the middle. While the glass will do as glass does and shatter, the plastic PVB the glass is stuck to will hold it together so it doesn’t shatter all over you and will keep extra damage at bay. This is why when you see severe damage on a windshield it looks almost dented. The PVB is usually slightly tinted as well to provide protection against UV, or ultraviolet, rays.
Tempered glass is what’s used everywhere else on your car; the backlight, or back windshield, and the sidelines, or the doors and other little slivers of glass. This glass is strong, but not as strong as laminated glass. The term tempering refers to the rapid heating and cooling of the glass to strengthen the glass 5 to 10 times more than it before it’s tempered. The reason the glass on the sides and back of your car does not need to be as strong as the windshield is a failsafe for your roof in the case of a rollover collision; another glass is not. Also, if for any reason there are children or animals (or you’re your keys) locked in the car, the glass is not too hard to break.
All glass in your car is shatterproof, or at least sharp, jagged, painful shatter shatterproof. Tempered glass doesn’t have a layer of plastic on the inside in case of emergencies, but because of the way it is tempered, when it’s broken it shatters into little dull shards that won’t cause any real harm to a child, animal, or anything that may be in the car. If you want to know more about how laminated and tempered glass is made, check “this article (insert hyperlink)” out for more details.