I swapped my FOIS Speedmaster's sapphire crystal with an Omega hesalite (plastic) crystal and it's the best modification I've ever made with any of my watches.
Once I found a watchmaker in USA that was familiar with this switch from sapphire to hesalite crystal, I pulled the trigger. Boy am I glad I did.
My hesalite acrylic crystal FOIS Speedmaster was successfully pressure tested to+6.0 bar without any problems. The improvement in my FOIS aesthetics and character once switched to hesalite crystal is simply unbelievable. Words cannot describe this enhancement. I love it!!!
The watchmaker at Clock Doctor in Scottsdale said that the hesalite trade is completely reversible without any case modifications required. He pressure tested my FOIS to +6.0 bar. Here are before and after pics:
Sapphire crystal
Hesalite crystal
