What kind of eye protect is appropriate for glass fibre insulation but won't fog up?
They make a spray for Hockey visors that prevents them from fogging up; I have never tried it on goggles, but it should work on goggles too. It always kept my visor fog free, and I was always hot and sweaty playing hockey.  You should be able to find it at your local sporting goods store.

Actually I can't believe I have never tried this, I'm going to spray my safety glasses right now.