I have been thinking about doing some fiberglass projects myself and have been searching for an "impact friendly" material
that is not Urethane. I havent found it exactly, but i did come across some flex resins
http://www.reichhold.com/composites/...logy.cfm?ID=35. I think if that was combined with some regular rigid resin, and had two layers of carbonfiber(you could use regular glass) with a lyer of kevlar smushed inbetween; you would have a pretty damn strong bumper that would be lighter than urethane.