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Norwegian here, when I was i the army up in the fucking cold north we got net underwear that we always used both upper and lower body. Transports sweat away from the body and thus making you keep your heat.
It works perfect for cold condtition because if you sweat out your clothes you will 100% freeze. So instead of constantly removing/adding layers you can just use netting and don't be *that* worried about freezing, even after your activity level drops, when having a break or something.
Bought some of these after the army because of how good they were, you never even have to remove them when out on a long hike. Perfect for layering, just add a wool sweater on top when stopping so you don't loose your body temperature quickly.