Anyone got cold weather camping tips?

[Edwards]

The first thing you need to do is acclimate your body to the cold. I used to work outside all year working longer hours in the winter.
I found that after a couple of weeks I could not stand being in a heated room and this was even painful if going in from being overnight outside all night in the morning.
Lots of calories and wear the right sort of clothing, cotton boiler suits breath but when it is really could do not get wet with the correct insulation under them. A winter Duvet coat is a good idea as you can put it on quick but you would need the water resistant outer.
A fleece inner sleeping bag is a usefull item to use as when it is really cold you can freeze the moisture out then shake it off.
Look at some of the military Arctic kit for ideas but remember that most of their stuff is only intended for a few weeks cold use at a time.

[Graham O]

A fleece inner sleeping bag is a usefull item to use as when it is really cold you can freeze the moisture out then shake it off.

NO! Not an inner bag in very cold conditions. Your main insulation layer, i.e. down sleeping bag always goes nearest your body and the source of moisture. Putting the extra insulation on the outside moves the dew point further out in the main bag or ideally into those extra insulation layers. Any ice build up will then occur in the extra layers, not in your main bag. Consider that it is +15C inside the bag and -15C outside. 0C, where ice forms, is at some point inside the insulation, down or synthetic. By putting extra insulation on the outside, you are not just adding warmth, but hopefully moving the dewpoint further out when even just a sunny day can help dry your bag. It's also worth going for dark colours to absorb any of the sun's heat.

[HPFlashman]

What about the vapourbarrier sack ?

My own horrible translation of the Norwegian Dampsperrepose but those where all in vouge some years ago. Primarily made for not letting bodycondense leak into the sleepingbag.

I have no experience with those things myself, as my coldcamping (iow non warmed up bivvying) have been mostly for 3-5 days and longer stays have been with some sort of oven heating in the tent, either kerosene or woodburning stoves to go.

[Graham O]

Vapour barriers work in 2 ways. Firstly, they keep moisture from your body from entering the insulation of your sleeping bag and secondly, by preventing evaporative cooling from the body, (the main mechanism for controlling body temperature) they keep more heat inside the sleeping bag. So you sleep hot and clammy as the moisture builds up, but with a good wicking base layer on, comfort is not okay. I've only used an internal vapour barrier liner and it was very hot and sweaty, but conditions were not -20C or lower.
An external vapour barrier does the same thing to prevent moisture from the outside, i.e. cooking or melting snow, getting into your sleeping bag. This is a new idea and initial testing last year showed that it works. I'll be sending more gear up to the Arctic for testing this season. This will be a Thinsulate outer bag plus inner and outer vapour bags. It should extend the warmth of the sleeping bags down to -55C.

[shane]

Fascinating if slightly sweaty stuff , Not sure I'd be too comfy sleeping in my own sweat but I guess its better than dying .

I was thinking of using a lightweight bivvy as an outer to keep that condensation off the bag(s) I gather they're quite cheap nowadays so I can throw my rather too thick and heavy army one out

[Edwards]

Fascinating if slightly sweaty stuff , Not sure I'd be too comfy sleeping in my own sweat but I guess its better than dying

At really cold temperatures you should find you do not sweat that much in the sleeping bag. In Northern Europe and Russia an old method used for sleeping was some form of layering system.
As has been said the temperature drops dramatically away from the body, thus the skill was to use layers of insulation so that the freezing point was ideally one layer that could be kept frozen or at least have the frost shaken off.
Loose Ventile frost covers used to be used as the outer shell for any condensation to freeze on, the one problem with this material is the fibers swell and tended to hold any moisture in (if it got that far). Again this layer once frozen was idealy kept that way.
Modern lightweight nylon would probably perform better, I do not know as I have never had the opportunity to test the Ventile.