The two main shapes of sleeping bags are mummy and rectangular. These two types can each be classed in two further categories: down fill and synthetic fill. So, in essence, there are four types of sleeping bags: Mummy/down filled, mummy/synthetic filled, rectangular/down, and rectangular/synthetic.
Mummy bags insulate more effectively; rectangular bags permit more movement and comfort. If you camp only in warm climates, a rectangular bag is your best choice. If you camp in varying temperatures, it is best to own a rectangular bag for warm weather and a mummy bag for cold weather. If you are planning to summit Rainier, get a mummy bag. If you need to bring a bag to a camp lodge for a church retreat, get a rectangular bag.
Down filled bags weigh less and provide better insulation than synthetic-filled bags. They also compress into smaller shapes and tend to be of better quality. Synthetic-fill bags cost less, and a wet synthetic bag works better than a wet down bag. (I don’t recommend testing this, by the way, but if you hike through a rainstorm, this might become an issue)
III. Evaluating and comparing sleeping bags
Compare each bag for:
Temperature or comfort rating
Total overall weight
Size when compressed as much as possible
Overall size
Type of insulation
Type of compression bag included
Temperature or comfort rating describes the minimum temperature the bag is designed for. A bag designed for 50º is really only suited for comfortable sleeping in warm weather. A bag rated at 0º is ok for winter camping, but you would sure want to be inside a tent or bivvy sack. The ratings the manufacturer provides are only a guide. Some people sleep quite comfortably in a 40º bag at 20º, while another person will shiver in 40º weather in a bag rated to 20º. If you’re the type who needs flannel pajamas and an electric blanket in October, you need to compensate for that. If you sleep in a tiny silk teddy and — ahh, nevermind.
Prepare for cold. Select a bag with a temperature rating that exceeds the low end of the temperature range you expect. If a +20° F bag sounds right for you, a +10° bag would be better. You can always vent the bag. Vent the bag? That’s a fancy way of saying “undo the zipper a little bit.”
Look for a bag rated +35° and higher for summer camping, +10° to +35° for spring and fall, a 0º bag for cold weather or high altitude, and an “Extreme” or -10º bag for winter camping. This is just a guideline; most of us can’t afford four different sleeping bags, and even if you can, there are 10,255,672 more sensible things you can do with your money. (I personally own one bag with a 40º rating and one bag with a -10º rating. I compensate with less or more clothing as needed.)
Total overall weight, or, how heavy is this thing I have to schlep around? You may find a great deal on a 0º bag, but if it weighs nine pounds, you will need to call a chiropractor into camp after a day of hiking. Some bags say “Fill weight 3.5 pounds” which sounds great, but how much does the rest of it weigh? Four — maybe five — pounds is the most you’ll want to carry — probably 10 to 20 percent of your total packweight.
Size when compressed. If the thing is lightweight but huge, keep shopping. Besides the awkwardness, if your bag is so big that it brushes the poison ivy on your way down the trail, well, keep shopping. Remember that down bags compress to half the size of a similar synthetic bag.
Overall size is not to be taken lightly if you’re a large person. Do you need a “regular” or “long” model? The general rule is as follows: If you are no taller than 6 feet, choose a “regular” length bag. If you are up to 6-feet-6, you want a “long” bag. If your waistline is more than 40″, you want a “long” bag. Remember also to find out if the bag is designed for male or female. At the low end of the price scale, most tend to be unisex, but among $175 and up bags, they are often differentiated. Now, most of us guys are secure enough that we could care less if we buy a lavender bag. But when it won’t fit, that’s a whole different matter.
Type of Insulation Down is the wispy, fluffy undercoating found just beneath the outer feathers of geese and ducks. This natural fiber is an extraordinary insulator. As mentioned above, it provides outstanding insulation for very little weight, and can be compacted into very small sizes. Down sleeping bags will last decades. One of the fellows I backpack with has a down bag he bought in 1969 that keeps him a lot warmer than my high tech synthetic bag, and his bag takes up half the pack space. Down is graded according to “fill power,” which is the number of cubic inches one ounce of down will displace. The higher the number, the better the insulation.
Synthetic fill is thin, extruded polymers, which is a fancy way of saying plastic. Its advantages over down is that it still provides some insulation when wet, it costs less, and is non-allergenic.
Type of Compression Sack
When comparing costs, note whether you are being provided with a compression sack or simply a bag for your sleeping bag. The compression sack will allow you to minimize the size of the bag, and a good compression sack will cost well over $10. If you don’t plan on backpacking, and you have one of those monster SUVs with plenty of room, you don’t even need a stuff sack. Note that some bags have an integral stuff sack attached to the foot area. This is convenient, but not necessarily an advantage if you wish to “hang food” or create an ersatz pillow using the sack.
IV. Keys to Comfort
A good sleeping pad is essential. Your body compresses the underside of the bag, squishing the insulation and making it much less effective. For snow or frozen ground, use two pads.
Eating before bedtime may also help improve warmth. An active metabolism will elevate the temperature inside a sleeping bag.
Keep your tent closed tightly. This will keep the temperature as much as 10º higher on a moderate night, and will feel up to 30º warmer on a sub-zero night.
Dry long underwear, clean shirt and clean socks are important on cold nights, plus they help keep body oils off your bag which will improve longevity.
Look for a bag with a double zipper if possible. This will enable you to ventilate the foot area if you feel too warm, yet you can keep the rest of the bag zipped
