[NOTE: this post is about proper sleeping bags, excluding liners, blanket systems, and quilts]
I’m currently in the market for a new sleeping bag. New gear! So much to consider. I’ve used the same bag for over 10 years. My current bag is a Coleman mummy that my parents bought me when I first became a Boy Scout. It’s a good 3 season bag, probably 25 or 30 degrees F. I’ve found, though, that it’s not as light or as packable as I’d like. This hasn’t been a problem so far I’ve just used my liner on long trips. But now that I want to do more 3 season backpacking, I figure it’s time to replace the bag.
There are really 5 factors that go into choosing a sleeping bag:
1) Cut – Most backpackers will opt for a mummy style since it saves on weight and volume. If you’re just car camping you might go with a rectangular or semi-rectangular cut.
2) Fill – Down or synthetic? A tough choice for some, others swear by their choice. The problem is, there are zealots on both sides. Down keeps you warmer with less filling, is lighter, more packable, and generally lasts longer than synthetic filling. It is a little amazing that we still haven’t developed a fiber that matches down feathers in these respects. That said, down doesn’t do as well as synthetic fiber in damp conditions and down bags are more expensive. Lots of things to weigh (!). But if you have a mild allergy to down feathers (like me) the choice is easy for reasons beyond such calculations.
3) Temperature Rating – When will the bag be used? Summer-only (rating 35 degrees and up), 3 season (15 to 35 degrees), or also in colder conditions (below 15 degrees)? Every bag comes with some sort of manufacturer’s temp. rating. The accuracy of these ratings will vary according to sex, body size, tent style, whether you’re sharing a tent, whether you’re using a bag liner, what style of sleeping pad you’re using, etc. For instance, I tend to sleep warm, so I can usually sleep comfortably even if it drops 10 degrees below the bag’s rating. There are also independent ratings that help keep manufacturers honest about their own ratings…because sometimes the bags don’t turn out to be as warm as advertized.
4) Weight and Packability – Some bags pack better than others, and some are lighter than others. If you want a bag for backpacking, these two factors are especially important. The differences among bags are due to either the filling type or the shell. There can even be a great deal of variation among down bags or among sythetic bags, too – some down bags are heavier than other down bags and some sythetic blends weigh more than other synthetics. So even after deciding for (or against) a down bag it’s still important to pay attention to the weight specs.
5) Price – Simple enough. The problem is this: you can have a light bag, a cheap bag, or a warm bag – pick 2. If the price is held constant, as the temperature rating goes down, the weight goes up. If you want to stick with a low weight, as the temp. rating is warmer, the price goes up. And among bags with the same temp. rating, the lighter the bag, the more expensive. So these three factors – weight, rating, and price – are indirectly proportional.
I think I’ve settled on this bag – a mummy synthetic, with a medium temperature rating able to keep me warm even if it drops into the 20s, weighing about 3 lbs, with a pricetag of only $90 bucks.