Double layer glass is known as laminated glass or laminsafe glass. What is Lamisafe glass?.
Single layer glass also known as tempered glass (Temperlite). How tempered glass made?
Original glass is the glass make for the car, the different between original and none original windscreen click for more info.
This is some of the method to take care your windscreen. A good windscreen not even comfort your eyes, it also save your life.