The glass used in the windshield of your car is very different than the glass used in the windows of your home. When the glass used in the windows of your home breaks, it shatters into extremely sharp and dangerous shards. The safety glass used in a car windows will not. When it breaks, it is actually quite harmless.
Auto glass is either tempered or laminated. The glass usually used for the front and rear door windows and the rear window are made from tempered glass, the windshield is made from laminated glass.
Laminated glass can trace its roots back to the mid 1920’s, when the auto industry took two sheets of glass and basically stuck them together with a sheet of PVB (polyvinyl butyral) between them. The “sandwich” was fused together using high heat and laminated safety glass was born.
Laminated glass will break but it will not fly into shards during a collision. The glass is designed to take heavy impact without shattering. This eliminates the possibility of passengers being injured by flying glass. In the event the occupant in the car is thrown into the window, the laminated glass acts somewhat like a cushion.
Although laminated glass is used extensively in the auto industry, it can be used for any application where there is the possibility of impact by a person. Many shop windows are made from laminated glass just for this reason.
Although it is possible for the door windows and the rear window of a car to be produced from laminated glass, there is not the same potential for human impact in the event of a crash. Therefore, the majority of these windows are made from tempered glass. Tempered auto glass is single-ply, but it is treated by heating and then rapid cooling. In the event the glass breaks, it does not shatter into dangerous shards but rather into thousands of harmless pebble-like pieces that do not have sharp edges.
Just as laminated glass has applications outside the auto-industry, so does tempered glass. Tempered glass is an ideal material for products like baking and cooking dishes, sunglasses, and the screens used in some cell phones and tablets. The manufacturing process for tempered glass results in a hard and strong glass when compared to untreated glass of the same thickness. Because of the structure, laminated glass can be repaired if it chips or gets a small crack, this is not the case with tempered glass, when it breaks it needs to be replaced.