Selecting a sleeping bag
Choosing a sleeping bag for a backpacking trip is very subjective. There are several factors to take into consideration, temperature rating, shape, size and of course insulation
Down sleeping bag are lightweight, very compressible, and highly durable. Most quality down sleeping bags use goose down as insulation. While more expensive, a down sleeping bag will likely last two to three times longer than a synthetic sack, making down the economical long-term choice. Nothing beats down's softness or warmth-to-weight ratio. But keep your down dry—once wet, it offers zero insulation value. Down's insulation capacity is measured in fill power—the volume, in cubic inches, occupied by one ounce of the material. Down measuring 600 to 650 fill is excellent quality; the very best stuff can be 900.
Synthetic insulation retains their warmth even in foul weather. They are usually less expensive than down and are non-allergic. Sleeping bags made synthetic are easier to maintain. Synthetic insulations, won't compress as well as down but can be easily machine-washed and -dried.