Is it a film that's sensitive to something other than light - like long wave infrared or possibly UV?
I'm thinking perhaps the radiation polymerizes this stuff and so changes its properties.
Oh, I see it's already been guessed.
Tell me, oh Jeekins, what sorts of places do you hang out in that require such a heavy duty form of eye protection? Could it possibly have something to do with some stuff hitting the fan?
If we weren't meant to eat animals, then why are they made of meat?