Others may have more direct experience, but when I was a CFR/ARRF firefighter, I seem to remember Nomex was similar to cotton of similar weight (not like blue jeans) But that it died faster. However, I was never subjected to long term exposure.
If I flew a glider with gasoline on board, a surplus Nomex flight suit would be my first choice. Cotton second, and I never wear artificial fibers like polyester.
Way too flammable!
Good Lift,
Scott