On a new car, every part comes from the original equipment manufacturer (the OEM), including the windshield. For windshield replacement, you have the option to select a replacement made by a company that manufactures OEM windshields, or glass made from non-OEM manufacturers ("aftermarket glass"). Both OEM and aftermarket glass must comply with the Federal Motor Vehicle Safety Standards, but there are two important OEM benefits:
Safety glass is used in all automobile glass. It is manufactured to reduce the likelihood of injury, if it breaks. There are two different types: laminated glass and tempered glass.
Windshields are made from a lamination process. A windshield actually consists of two pieces of glass, bonded together by a vinyl inter-layer. This vinyl layer cushions your head during impact. If a windshield breaks during impact, the broken pieces will generally adhere to the plastic lining.
Side and rear windows consist of tempered glass, which is produced by heating the glass to more than 1,100F and then rapidly cooling it. This results in the outside surfaces of the glass becoming harder than the center of glass and, therefore, is stronger than regular glass of the same thickness. If broken, tempered glass will break-up into very small pieces.