One of the first decisions you’ll be faced with is this: down or synthetic? Here, the differences and pros and cons of both:
Down is the lightest, most efficient insulation you can get. It’s also the most compressible (a big plus for backpackers carrying big loads), and it retains its loft (and therefore insulating power) longer than synthetics. Down is generally more expensive than synthetic, but it also depends on the fill-power, which is a way of rating the quality of down. Fill-power ratings range from about 600 to 900. The figure refers to the number of cubic inches one ounce of down consumes in a beaker. And since the warmest down is the loftiest down, the higher the number the warmer you’re going to be.
There are many different types of synthetic insulation, but it’s generally a fluffy polyester material that doesn’t absorb water, making it a smart choice for any camper who might be faced with wet conditions. Although down bags are typically bulkier and heavier, they are much less expensive.
BACKPACKER Tips: Selecting the right sleeping bag shell fabric
This really only comes down to one decision: do you need a waterproof bag or not?
Only answer “yes” if you truly do need that level of protection: if you frequently camp without a tent, for instance, or you live in the Northwest where wet conditions are prevalent. If you decide you need a shell, you’ll pay for it (up to $100 more).
A waterproof bag must be shelled in waterproof/breathable fabric (much like that of your rain jacket). If the fabric doesn’t breathe, although you’d keep out the rain, you’d soon be sleeping in a puddle of your own sweat. Waterproof bags also need to be seam-taped, so water doesn’t migrate inside through the stitch holes.