So My duplicant took a magmaswim to prepare a volcanic oil boiler. He left behind a 4000gram tile of refined carbon and reported "toasty surroundings" but took no health dmg.
I guess the snazzy suits arent worn over the atmosuits, so in theory they should not melt unless the duplicant is also melting.
Another thing is, a duplicant without insulation takes health damage in an 80 celsius sauna, but goes out without a scratch from molten magma in an atmosuit. Maybe magma + atmosuit should also trigger scalding, while not carbonating the underwear.
Steps to Reproduce
Wear a shirt (4kg thimble reed) under your atmosuit. Take a bath in 1600 C.
This issue has not been confirmed by a developer yet.