karopak and anything else fiber is going to squish some.
the heaviest stuff i have is about .060 and crushes to about .050, i think it was called 'high temp gasket' at the auto parts store. they should have about 4 or 5 types at any good auto store, just feel them and see what is the heaviest?
if you need something really invincible the stuff we use for high pressure flanges at work is called 'garlock' and its very similar to flooring lineoleum, its completely huge and indestructable.