"For steel castings etc. where the mating surfaces do not flex, I would guess that a more spongy gasket might be best"
like a head gasket? ... or a thermostat housing gasket? ... or a trans side cover gasket?
gasket material depends on the "material" being contained as much as the mating surfaces - pressure, oil, grease, water, air
nowadays many gaskets can be replaced altogether w/ sealer, or 'liquid gasket maker'
Bill
