The only way to totally eliminate ice build-up in extreme cold is to wear vapor barrier clothing and breathe through a snorkel... a tube with a couple of simple flap valves for intake and exhaust (tube to the outside of the shelter) in the mouthpiece. Intake would not require a tube if there is some fresh air ventilation.
Jack Stephenson (of Warmlite fame) was known to expound on this frequently and at length, and it was he who
helped Will Steger address the serious condensation issues he confronted during his polar expeditions.
The snorkel might sound silly but if I were a serious adventurer spending protracted amounts of time in deep cold I would absolutely experiment with the concept.
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