Choosing a Sleeping Bag
Down is the lightest material relative to the amount of warmth it provides; however, it is a poor insulator when wet. Synthetic materials, on the other hand, provide warmth even when wet and synthetic sleeping bags are normally cheaper than down sleeping bags.
Select a sleeping bag that is 10 degrees (Fahrenheit) below the lowest temperature you plan to encounter. Keep in mind that temperature ratings always assume that the sleeping bag will be used with a sleeping pad.
Mummy shaped bags provide more warmth while rectangular bags provide more comfort. Dual zipper sleeping bags are an excellent choice if your feet tend to overheat.Full Article