Your car’s windshield is two pieces of float glass with a plastic laminate sheet sandwiched between the glasses. The reason for this is safety as windshields, which must withstand impact ratings. If a stone the size of a pebble hits your window, it will not penetrate the glass, even if you are going at high speeds. The main reason for windshield breakage is due to the stone getting between the treads of tires and is flung in the air bouncing off the road and into the glass. The angle and how fast you are going will determine the damage. Many people fear that because the glass is broken, the windshield will cave in on then. This is not exactly true since your windshield is two pieces of glass. The plastic lamination between them has protected the inner piece of glass.

The glass in the rest of the car is different since the door glass and the backglass are a tempered plate. It is just one piece of glass. While it does take quite an impact to break this type of glass, when it does break, it falls apart into hundreds of small glass beads. A good tempered door glass will not cut you but a poorly tempered glass will break in shards and can cut badly which is one of the reasons for choosing an OEM glass product.

Many people are amazed that one cold winter day or hot summer day, they came out to the car and all of a sudden they noticed a long crack running through the windshield, or the back glass is broken in a million pieces on your back seat. The windshield at some point had a small crack or bruise. The tempered backglass might have had a defect. Glass is very susceptible to quick changes in temperature. 

The biggest concern people have about replacing their windshield is breaking the original seal at the factory. If properly installed the new seal is just as good as the one done at the factory.