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The down side to glass? IT BREAKS!!! And when it breaks it can be nasty. Glass can cut like a razor. To counter this potential to injure, a lot of the glass in a car is what is known as "Tempered Safety Glass".
The big safety advantage to this is that whentempered safety glass finally breaks all that internal stress is released, and the entire piece of glass crumbles into tiny pieces, no bigger than 1/4 inch square. Thus it can't cut you like regular glass, which will break in long, dagger-like shards!! Most all the glass in a car is Tempered Safety Glass: EXCEPT THE WINDSHIELD!!! It is usually a laminated glass: actually 2 layers of glass with a layer of clear plastic in between. The plastic keeps the shards of glass together if the glass should break. There have been a lot of people hurt, disfigured, and killed by going through the windshield, SO WEAR YOUR SEAT BELTS!
Many newer vehicles use the windshield as part of the structural strength of the vehicle! (Remember: glass is very strong!) This is being done on more and more vehicles to save weight. Urethane adhesive MUST be used in cars where the front glass forms part of the structural strength of the car. Urethane adhesive comes in tubes that fit a caulking gun. It's pretty tenacious stuff. It sticks very strongly to glass and most anything else. Just about all modern windshields are held in with urthane.
A LOT OF A CAR IS MADE OF GLASS!
Almost half of your car is made of glass! Glass is an amazing substance. It's not really a solid: it's a supercooled liquid and has many amazing properties. Some are good qualities: It's very hard and resists scratches. It is very transparent and can be tinted. It is very strong and slightly flexible: Glass gets stronger the more stress you put on it!
TEMPERED SAFETY GLASS
When they make tempered safety glass, they rapidly cool the outside. This is the "tempered" process. This hardens the outside of the glass first and puts a lot of internal stress on the finished piece of glass. (Remember: glass gets stronger under stress! ) GLASS INSTALLATION METHODS
Glass is installed in cars several different ways:MECHANICAL FASTENERS WITH FELT GUIDE TRACKS OR RUBBER SEALS OR GASKET
These are found in windows that open (roll up) on a vehicle. In door glass, the glass is attached to a mechanism (called a WINDOW REGULATOR) inside the door which pushes the glass up and down. It is normally powered by either a hand crank or electric motor. Some vehicles (vans especially) have hinged windows with a latch and a rubber seal, or sliding windows. All of these use safety glass.
Used in windows that "roll up"NON-OPENING WINDOWS WITH GASKET
These windows are held in only by a rubber gasket. It surrounds the glass and goes over a metal flange in the window opening of the car body. Often used in the back glass of vehicles, sometimes in the windshields of trucks. This type of window is actually a safety feature: in a collision the rubber gasket allows the glass to "pop out", making it unlikely a passenger could "go through the glass" and injure themselves. In this setup the glass provides no structural support to the body. GLUED IN AUTO GLASS
This is normally found in the windshield and sometimes back glass of vehicles. 2 types of adhesive are used: a "Windshield Kit"and Urethane Adhesive. The old windshield kit stuff comes in a "rope", almost like putty, which you form around the windshield mount area. You then press the glass into it. It provides just enough adhesive force to hold the glass in place. Most older vehicles without a rubber gasket around the windshield use a windshield kit to hold the glass in.WINDSHIELD REPAIR
Most glass should just be replaced when damaged. Most of the time the "comprehensive" part of your auto insurance will pay for the job. For very small "bull's-eye" defects as well as very small "star" cracks in windshields there is another option. Several repair systems exist to inject a liquid acrylic into the defect and repair it. One website making that product is www.gtglass.com . I'm not saying this is as good as a new piece of glass, but if the damage is minor and the windshield is expensive this might be a good option. SCRATCHES
Scratches on glass CAN be buffed out with rubbing compound, BUT IT'S A LOT OF WORK!!!!
Remember! Glass is VERY HARD!