We found the best reviews of sleeping bags at Backpacker Magazine, which tests more sleeping- bag models than any other publication and reviews them several times a year. The summer buyer's guide issue of Outside Magazine is also based on field tests, but reviews fewer sleeping bags. Climbing.com compares 11 ultralight sleeping bags, and the older review at Backpacking.net is still quite useful because it's so detailed and thorough.
These comparison tests focus on lightweight three-season sleeping bags, but for summer car camping, many people prefer heavier but roomier rectangular sleeping bags -- including double sleeping bags for couples. We found the best reviews of this type of sleeping bag at retail sites that publish owner-written reviews. Reviews at Moosejaw.com and Amazon.com also include parents' reviews of kids' sleeping bags. Good Housekeeping provides an online video review summarizing comparison tests of 11 kids' sleeping bags, but the conclusions are based on tests done back in 2001, so new models aren't included.
This matters because newer sleeping bags use better insulation. Synthetic insulation has continued to improve in quality, with more durable loft and more warmth per ounce. This doesn't matter so much for summer car camping, where budget insulation can suffice. For backpacking and cycling trips, however, where every ounce matters, tests show that newer Climashield HL (for "high loft") insulation outperforms Polarguard Delta, which in turn was an improvement over earlier polyester fill. One of the models recommended in our chart, The North Face Cat's Meow (Est. $170 and up), has steadily improved the synthetic insulation used, and now uses Climashield, as does The North Face Tigger +20 (*Est. $60) kids' sleeping bag. The continuous improvements in the Cat's Meow sleeping bag have earned it two Editor's Choice awards at Backpacker Magazine.
Goose-down sleeping bags cost considerably more than even the best sleeping bags with top-rated synthetic fill. However, the best down sleeping bags hold their insulating power for decades if well cared for, so reviews consider them a long-term investment. The best down still has a better warmth-to-weight ratio than the best synthetic fill. Down bags also compress into a smaller size for packing, making them the best sleeping bag for any trip where they'll be carried a long distance.
The Achilles heel of down sleeping bags, however, is their response to dampness. Even moisture from body heat and condensation can lessen down's insulating ability, and once wet from dew or rain, a down sleeping bag can take a long time to dry. Synthetic insulation, on the other hand, not only dries fast but can keep you warm even while it's wet.
There are two basic shapes of sleeping bags: rectangular and mummy. In general, reviews recommend rectangular bags for summer car camping rather than for use in cold weather or for backpacking. Mummy bags use less fabric and fill so they're lighter – better for backpacking -- and the body-hugging shape holds in heat. You can still unzip a mummy bag to use it in warmer weather, so this shape is the most versatile. However, rectangular bags are roomy and comfortable, especially if – like most people -- you move around a lot in the night and often sleep on your side. Most double sleeping bags are rectangular, or you can zip two singles together to make a double.
Manufacturers give each sleeping bag a temperature rating – the lowest ambient temperature at which the bag is warm enough. Experts say to take this rating with a grain of salt because perceived temperature varies so much among individuals. Some people "sleep cold" and need a sleeping bag rated 10 or even 20 degrees colder than other people. It's better to err in the direction of getting a sleeping bag that might be warmer than you need than to shiver all night. You can unzip it to cool off.
Temperature ratings are the basis, however, for roughly categorizing sleeping bags by season:
Three-season mummy sleeping bags are the most versatile, since you can extend their use into even colder weather by adding a warm liner, inserting a Nalgene bottle of hot water and/or wearing more clothes to bed. Experts say a warmer sleeping pad can also make a huge difference on cold nights. (We have a separate report on sleeping pads.) However, most people prefer a rectangular sleeping bag for summer car camping, and it's also the least expensive choice.