poly is lower than the Fiberglass one, and unlike Fiberglass Urethane isnt going to break on a hard impact with a curb or street when you hit , but ureathne is not like superman or anything if you do hit something with enough force it will break. but in most cases Urethane is great if your scared of scraping and hitting bumps and stuff. i have had both front and i like the Urethane way better. also the Urethane is heavier. also i muight be selling my Urethane front so if your interested please pm me.