Here you go;
The two most common plastics used to make windshields are acrylic, which goes by the trade name Lucite or Plexiglas, and polycarbonate, also known as Lexan. Despite the similar-sounding names theyíre different enough to justify knowing more about them before you pick a windshield.
Acrylic is the shinier of the two and the least expensive, but it cracks or shatters easily on impact compared to polycarbonate. In any application where the windshield is meant to protect you from flying debris or where itís exposed to the same, acrylicís lower cost is offset by the likelihood of it exploding into pointy shards if itís hit hard. On the upside itís more scratch resistant than polycarbonate, so itís easier to keep looking new.
Polycarbonate is a lot tougher than acrylic. While acrylic is about eight times stronger than untempered glass, polycarbonate is about 200 times stronger. Itís used in DOT-approved helmet face shields, as well as racecar windows and machine-tool safety shields. Laminated layers of polycarbonate can even be used to stop bullets, though you donít want to annoy anyone that much if all you have between you and a high-caliber argument is a motorcycle windshield. Polycarbonate is easier to scratch, but windshield manufacturers get around this by adding a protective layer of hard-coating.
Hard-coated polycarbonate is pretty much the current state of the windshield manufacturerís art. The hard-coating is getting better, too, according to National Cycle, which says its proprietary Quantum process is 10 times more scratch resistant than the original hard-coated polycarbonate and 30 times more than acrylic.