Your sleeping bag is your happy place. You curl up in it at night and dream of peanut butter, massages, and a cold beer. Picking your bag, therefore, is a very important process. Much of the process boils down to personal preference and what feels right for you, but there are a few key factors that merit careful consideration: weight, compression, fill, style, and temperature rating.
Weight: The ever present gear question. If it is going to go on your back, on your bike, or in your bag, you should probably be conscious of how much it weighs.
Compression: We all know how big a sleeping bag gets when it is fully lofted, roughly the same size as your body. You definitely don’t want to be carrying around an object that big in your backpack. That is why compression is so important. How small can you make your sleeping bag? Size of a softball? Basketball? Baseball? Knowing the answer will help you decide what pack to use, how much other gear you can bring, etc. In general, you want the biggest bang in the smallest package because then you have room for all kinds of other stuff.
Fill: Down or synthetic. Nature got it right with down. Down’s ability to loft, insulate, and rebound from stuffing after stuffing is incredible. Its only downside (ha) is that it loses much of its loft when wet. Many outdoor gear companies have been searching for the perfect down treatment that negates this problem, but a foolproof solution still has not been found. Synthetic insulation is as close as science has been able to get to the wonders of down. It compresses exceedingly well, insulates when wet, and can be relatively lightweight. I have no doubt that the two will soon be relatively on par with one another.
Style: This used to be a simple question. For a long time, sleeping bags were either mummy bags or rectangular bags. For decades, mummy bags have been the go-to choice for outdoor-oriented consumers. This is largely because they cut down on weight and are significantly warmer. The beauty of a mummy bag is that your body doesn’t need to heat excess space. They are contoured like our bodies, which are not rectangular. In recent years, sleeping bags have evolved beyond the limits of either of these two designs. The mummy bag is still a hallmark of the outdoor world, but ultralight quilts and backless sleeping comforters are becoming very popular. Quilts are a very versatile piece of gear. They can be used like a blanket, partially connected, or fully “mummified”. Backless sleeping bags or sleeping comforters generally have a sleeve or webbing system for securing a sleeping pad to underneath the bag. This allows the insulation of the pad to take the place of excess insulation from the sleeping bag, cutting down your overall weight.
Temperature Rating: This is probably the most obvious question when it comes to sleeping bags. How cold can it get for me to still be warm in my sleeping bag? This question, again, depends largely on personal preference. If you sleep hot, then a 20° bag will get you farther than someone who sleeps on the colder side. 10-20° bags are often considered 3-season bags. 40° is a good summer weight. Anything below 10°s is getting into winter and that fringe season between fall and winter. The temperature rating on your bag should not necessarily be seen as a limiting factor. You can wear a down jacket and fleece pants in a 20° bag in 10° weather. You can also throw a liner (silk or poly) and a bivvy over the top to make an all-weather, any-temperature shelter.
Go forth and research.