big difference
There is no comparison bettween Lexan (or any other manufacturers Polycarbonate sheet) and Plexiglass which is an extruded Acrylic sheet. I believe Lexan was developed for fighter canopies. You cannot break Lexan. I have seen guys take a ball peen hammer to it and it simply WILL NOT crack, shatter, etc. Plexiglas on the other hand WILL crack, shatter, etc. Home depot sells Acrylic sheet, that's why it is so cheap. Your OEM windshield is laminated with a plastic layer in the middle that adheres to the glass and retards glass fragments form entering the vehicle with any breakage. NEVER put anything but Lexan (Polycarbonate) in a windshield application. Anything but Lexan would be very Dangerous!!! From a safety standpoint, I wouldn't use Plexigas for anything on a car. Your side and rear glass is tempered so that if it breaks, it crumbles and there are no shards of glass. Plexiglass will shard, and therefore is dangerous in an automotive application. You will have clarity problems with anything but glass. That is just the tradeoff for the weight savings. You can either live with it, or you can't.
Dan