FWIW, I just got a pair of these, and they are polycarb.
http://www.safetyglassesusa.com/essice243len.html
and have the prescription insert on order. I wanted something that seals out dust and bugs really well, and these work. At $42, they're not as cheap as some of the others but it's a good system with everything replacable if it gets scratched up or broken. In fact my optometrist sells exactly the same thing for $200 (not to me though). I ordered the prescription from them for < $100.