There is nothing worse at night than cold. Remember that a sleeping bag is your best friend during the expedition, so you must take good care of it. I suggest avoiding ones with acrylic fibre filling - they are heavy and not really warm. So called 'artificial down' is a better solution, but the best one is real down - from geese, ducks, or hens (in this order). What is important, even if your clothes are damp when you crawl into a sleeping bag filled with natural down, they will be practically dry in the morning. Bear in mind, though, that down itself should not remain damp. The sleeping bag should be aired and dried – not necessarily first thing in the morning, but the sooner the better. Only then will it serve you for a long time. The sleeping bag should have a "mummy hood". If your head is not covered and the night is cool, you can lose up to 50% of body heat and develop hypothermia.