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If you’ve ever seen a picture of a driver behind the controls of the earliest automobiles, you might notice that they were just sitting out in the open. There were no cabins, let alone windows. This is why the earliest drivers wore goggles and heavy coats to protect themselves from the elements. Thanks to the implementation of car windows and windshields, we don’t have to bother with those anymore. When cars first got windshields, they were made of the same ordinary glass that you’d find in the windows of your home. 

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This wasn’t the best idea, as any manner of small, sudden impacts would instantly shatter them. This is why our cars now have specialized windshields and windows made of carefully formulated glass and other materials.  The windshield of your car is made up of laminated safety glass, a layered construction that can endure strong impacts with cracks rather than shattering. The other windows, meanwhile, are made of glass that’s been tempered by cycles of extreme heat and cooling. This makes it stronger than normal glass and keeps jagged edges from forming when it’s broken.

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Rather than a single sheet of glass like you have in your window at home, laminated safety glass is actually made up of two sheets of glass with a layer of clear plastic sandwiched in the middle. These three layers are tightly packed together to ensure that there aren’t any bubbles or air pockets between them, then the whole thing is pressed and heated until it’s merged into a cohesive whole. The result is a sheet that’s not only noticeably thicker than single-pane glass, but much tougher as well.

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The multiple layers of laminated safety glass help to absorb and dampen kinetic energy from sudden, strong blows. Where a normal pane would shatter completely, laminated safety glass just cracks outward from the point of impact. The reason why this particular glass is used for forward-facing windshields is obvious: it’s the most important window for both your vision and safety. If a chunk of debris comes flying right at the front of your car, the windshield will intercept it. It might crack, but it should stay intact. Granted, cracks and chips are still a problem, and you’ll want to protect your windshield in winter, but overall, it’s still the safest kind of glass to use.

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Your car’s windshield is typically the only window that’s made of laminated safety glass. The other windows in your car, including the side windows and the rear windshield, are made of tempered glass. Tempered glass is initially created much in the same way as a regular sheet of glass, with various minerals mixed, heated, and pressed into a solid slab. The difference is that the glass is then heated to temperatures of above 1,000 degrees Fahrenheit, then swiftly cooled back down to room temperature. This rapid temperature shift helps to reinforce the glass, strengthening it by several degrees of magnitude more than the ordinary glass it once was.

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While it’s not quite as strong as laminated safety glass, tempered glass is still much stronger than regular window glass and more than strong enough to endure the bumps and rigors of the road without cracking or shattering. Tempered glass is more likely than laminated glass to shatter completely if it receives a sudden impact, but it  beaks into small chunks rather than jagged shards, which is much safer for any passengers in the car. This is why tempered glass is also used to make glass desks safer. Unlike a windshield, which is supposed to stay intact in most circumstances, it’s actually important that a passenger window can still shatter. In the event of an emergency, you need to be able to break it and climb out, after all.

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