I thought I read proprietary mineral crystal in an earlier post. Can’t see sapphire as an option with the cost. I’d be good with acrylic too. If it was good enough then, it’s good enough now.
Seems acrylic flex is what helps with depth rating so not sure a stiffer crystal material is that desired unless people are really gonna beat on these things and see more scratches than from just desk diving. Polywatch is our friend.