One subject that often comes up, is the wearing of clothes in your sleeping bag.
Now I could write several chapters on this, but a brief breakdown would go like this: Never wear any wet or damp clothes inside your sleeping bag, be that socks or underwear or anything. Also be aware that moisture that is held in your clothes – that is at body temperature – will be invisible until it cools (this is why you can go to bed warm, and then get really cold). If you have damp clothes, then you should arrange them either over the top of your sleeping bag or over the top of your naked body inside your sleeping bag (the latter will dry them).
Wet clothes should be rung out, spun around your head, dried over a fire/stove, and then either laid on to of or placed under, your bivvy bag (wet clothes will act as an insulating layer). If you don’t have a bivvy bag, you can make a waterproof barrier by using your shell jacket, tarp etc.
The only wet/damp kit close to your skin should be socks and gloves, which should be placed in your armpits or groin. Never wear damp socks in the hope of drying them, and ideally, you should always carry either spare socks (todays dried damp socks become tomorrows sleep socks), or carry synthetic booties.
Never sleep in any kind of membraned clothing (gore, non-softshell softshell), as moisture will just be held within that layer, leaving you sleeping like “boil in the bag” rice, only without the boil (this is also why you never sleep in your boots).
True softshell (pile fleece), works well inside a sleeping bag when worn next to the skin, as the pile is very effective in moving moisture away from the skin.
Ideally, you should always change into a set of dry underwear for bed, and go to bed warm and well-fed and watered, and be aware that night warmth is a finite thing, it is the most precious thing in the world at 3 am, and must not be squandered or taken for granted.
Image: Neil Chelton, hanging out on the Russian direct on the Eiger NF.