In reply to Fredt:
Where are you heading? Do you want to be comfortable or just get some sleep? Bear in mind that even though in places temperatures 'can go down to -10' it doesn't mean they will, so you can have a compromise of weight savings and risking a couple of cold nights.
My 2 pence worth (most have been mentioned, but for the sake of grouping it tohgether...):
- Silk liner - Effective but probably not necessary, specially if weight is an issue.
- Pertex outer - (Bivy bag in general) Indispensable if bivying out. Not only it increases warmth a little bit but stops the wind stealing your precious warm air.
- Wearing clothes - Yep, when weight is an issue i factor in clothing in my sleeping kit. To carry clothing and then take it off to get in a sleeping bag that is heavier than it should is taking luxuries, plus the action of taking clothes off makes you lose on precious body heat.
Wear everything but belay/down jackets in the bag. I found that wearing heavy insulating clothing in the bag makes you colder than not wearing it, as it stops the body heat warming up the inside of the bag and makes you feel very cold in the legs, head, feet and hands. They work better on top of the bag like a quilt, between the bag and the bivy bag is best.
Put your gloves in your feet (handy to have long cuff gloves, if you carry mitts here is where they come on their own), put your hood on, make sure you close the bag tight around your neck/head and cinch tight those shoulder baffles.
- Hot water bottle - One of the niftiest tricks for sleeping warm. Using an Evian bottle or similar allows you to hug it for extra sweet dreams... A pee bottle is equally effective but don't mention it in the pub. A poo-tube doesn't work, so don't try it!
- Food/drink - Eat well before going to sleep, from inside the bag if possible (Like, when you are inside, not with the head in). Slightly fatty foods are best to keep you warm at night, such as meat sausages, cheese, olive oil, etc. Being well hydrated is very important, but if you drink too much too fast you'll have to get out the bag to pee, which is counterproductive to a warm night. Start drinking slowly from the moment you stop, and go to the loo before nap-time.
- Sleeping mat - Important to have a decent one. Foam pads are warmest and lighter, but you won't look as cool as someone with the latest £100 inflatable gimmick. Get them back by laughing at them when they get a puncture. Sure to warm you up inside.
If snowy bivy stick the pad inside the bivy bag. If you leave it out snow will pile between you and the mat which is like having no mat at all. Even if not snowy do so, as it stops you ending up outside the mat and waking up shivering.
If you have a foam mat as you should, and your bivy bag is one of the mummy shapes alpine style bag, then chop it to shape to fit in (the mat, don't chop the bag!). Extra points for weight saving and the alpine warrior look.
- Good spirits/attitude/psychology - Yep, the most important part of having a good night. Accept the cold and convince yourself that is not that bad. Think how this cold means you are sleeping out somewhere wild rather than a Holiday Inn in Skegness. Smile and count yourself lucky that you are 'privileged' enough to be there. Learn to enjoy it. When/if it get's too much tell yourself that is only a momentary inconvenience which will pass in a few hours. Don't think on it and relax, your body will get the drift that you are ignoring it's warnings after a while and stop pissing you off.
In the wise words of 'GhostDog'...
"There is something to be learned from a rainstorm. When meeting with a sudden shower, you try not to get wet and run quickly along the road. But doing such things as passing under the eaves of houses, you still get wet. When you are resolved from the beginning, you will not be perplexed, though you still get the same soaking. This understanding extends to everything."
Happy camping!
