There are three types of windshield glass that can be used on your vehicle; dealer glass, aftermarket glass, and Original Equipment Manufacturer (OEM) glass.
When purchasing dealer glass, it’s coming directly from the dealership who’s authorized by the manufacturer to work on your vehicle. Now this class will be the same type of glass your vehicle had when coming off the assembly line.
Original Equipment Manufacturer (OEM) means the parts are certified genuine manufacturer parts for your vehicle. In this case OEM glass is just like dealer glass because OEM glass will be the same type of glass as if your vehicle came off the assembly line as well.
Some glass brands may be different, but this really does not make any difference. If you have an older vehicle like a collectors car, then repairing or replacing anything with OEM parts retains the vehicles originality.
Aftermarket glass is manufactured by companies that deal directly with the car manufacturers. Although aftermarket is not OEM, it is made to the exact same specifications of OEM or dealer glass, but is not at all considered to be the original equipment. Also aftermarket glass is considered to be less expensive, its still typically is the same thickness from the original glass in your vehicle and carries the same guarantee as OEM or dealer glass.