Sorry for your troubles, ncvarmint2016, but thanks for posting. I did not think my new FW3T came with a glass lens, but after reading your post, I checked again and it fell out. Must have been stuck to the optic when I first opened it.
No one has yet mentioned, so I will suggest borosilicate glass, which Corning's
Pyrex is made from. It is probably the strongest glass next to Corning's
Gorilla Glass. Many flashlights have lenses that are made from borosilicate glass. flashlightlens.com sells Borofloat lenses with antireflective coating, and they are made of borosilicate glass.