Sleeping Bags: Ratings, Types, Care, Recommendations

There's no such thing as one perfect sleeping bag. If you do a lot of camping, you may end up with a couple. The major factors that go into picking the right bag for the trip are temperature rating, construction, and materials. But choice of ground pad as well as how you clean and store your bag will make a difference in how well it holds up for you.

Temperature Rating

The first thing people talk about is the temperature rating of their sleeping bag. In the past, temperature ratings where at best rough guides, but in the past few years, the European Norm 13537 (EN) rating system has been adopted widely as the standard and reliable way of rating sleeping bags. The EN rating actually include 4 temperatures, but most EN rated sleeping bags will have three listed: comfort, lower limit, and extreme. The comfort temperature is the lowest outside temperature at which an average adult women will sleep comfortably. The lower limit is the lowest outside temperature at which an average adult man will sleep comfortably. The extreme temperature is a nominal lowest temperature at which an average adult woman can survive (not at all comfortably). All ratings assume the person is sleeping in a single layer of long underwear and wearing a hat while sleeping on a 1-inch thick insulation pad. (The actual standard is very specific about the range of thermal insulation values the pad can have for testing, it's gets quite technical....)

In principle, when using the EN 13537 method, bags with the same rating should be very close to the same in terms of performance for you. Given the same temperature rating, construction and materials will make a difference in weight. 

Construction and Materials

There are down bags and synthetic bags. There is goose down and duck down. Most (all?) synthetics are various types of polyester fills differing in (microscopic) shape of the fibers and how the fill is assembled. Down is rated by its fill power which is a numeric rating of how much volume a given mass of down occupies. The higher the fill power, the better the insulation for the same weight. And the more expensive.... Goose down is capable of higher fill powers than duck down, but for a given fill power, both will do exactly the same: fill power is fill power regardless of the source of the down.

There are two many different synthetics to cover. They are not all the same, but when shopping you'll be looking for a trade off between cost, weight, and termperature rating. The lower the temperature rating, the more the bag will cost, but that's not usually the biggest issue. The lower the weight the more the bag will cost and that's where it will really hit your wallet.

There are a few different sleeping bag styles. The two most common are the rectangular shaped bag and the mummy bag. The mummy bag will keep you warmer since it has less internal volume that your body heat needs to warm up. However, you'll want to pay attention to a few things on a mummy bag. First, mummy bags are designed to fit snug. Some will specifically say they are cut larger to give you a bit more internal space. If you're aging (like me) and starting to fill out in the middle, get a looser cut. Second, the foot box can be very different. Some are square boxes, some are trapezoidal. If you tend to sleep on your side, the square box is fine. If you sleep on your back, you'll probably want a trapezoidal foot box which allows your toes to flop outward without putting pressure on the bag (stretching it tight) which allows heat to seep out more easily. Third, cold weather bags usually are sewn in styles called baffles, shingles, or quilted layers, to preven cold spots. Fourth, there may be additional features, especially on extreme cold weather bags, to limit heat escape such as draft tube along the zipper line, a draft collar just below the neck line, and a hood with a draw string.

Some sleeping bags come as part of a multi-bag modular system; the multiple bags are intended to next within one another when in use allowing you to take all or part of the set for a particular trip.

Ground Pad

Often neglected in the discussion of sleeping bags is the ground pad. The EN 13537 standard specifies particular insulation values for the ground pad, but I don't know of any ground pads that specify their insulating properties in the units of the EN 13537 standard or even reference it.

In general, a closed-cell foam pad is your best all-around ground pad for all but the coldest conditions. In warmer weather, an inflatable is nice since they will often give you a thicker cushion for similar weight. However, closed-cell foam is cheap. For extreme cold, using two pads will prevent body parts on the ground (back, sides) from getting cold. The standard foam pad is 3/8-inch thick, weighs about 1 pound, and costs about $20. There are variations with reflective mylar on one side, egg-crate patterns, and more that can slightly improve the thermal properties, but none of these are that great. Buy two for extra padding or cold weather.

Storage

Sleeping bags keep you warm by trapping air, warmed by your body, and slowing it's escape to the environment. To do that, they have to be fluffy. Every time you stuff you bag into its sack or compress it in the bottom of your pack, some of the fibers that make the bag fluffy get damaged. Down tends to be more resilient, but it too suffers from stuffing and compressing. When not in use, sleeping bags should not be stored in their stuff sacks and most definitely not in compressed compression bags. Ideally, bags should be stored they way they are displayed in the store, hanging in a tall closet someplace. But few of us have that luxury. Some of the more expensive sleeping bags come with storage sacks which are just large mesh bags you can hang on a hook. These storage bags allow the bag to expand so the fibers are not compressed which in turn helps them last longer. Mesh bags can typically be bought at discount stores for a few dollar, or the more expensive ones at sporting good stores (mesh equipment bags). We separate the components of our multi-bag modular system in and store part in a large mesh bag so the bags can remain uncompressed.

Cleaning

You'll need to see the instructions that came with your bag. Down bags require special care and you'll want to make sure the cleaner you take it to knows how to handle it. For synthetics, you can usually wash them in a front loader. Be aware that every time you wash your bag, down or synthetic, it's doing damage to the fibers. So the short answer to "how do I clean my bag" is "try not to get it dirty." If the weather allows, you can include a bag liner on the inside to keep sweat and body oils from soiling the inside and a bivy on the outside.

Packing

This really goes under the heading of "how do I pack my backpack" but I'll mention two things. For the first option, you can use either a stuff sack or compression sack for your sleeping bag. The main reason for using one of these would be to have a water repellent bag to help keep the sleeping bag dry. A compression sackhas the advantage of letting your really squeeze the air out and shrink the volume used in your pack. A second option it to just put your sleeping bag at the bottom of your pack. After you start loading things on top of it, it will end up naturally compressed for the weight of those things and you save the weight of your stuff/compression sack.

Recommendations

Because Troop 13 camps year round, you're going to need a sleeping bag that can keep you warm in cold temperatures. In the coldest months, we usually try to find cabins, but sometimes we'll be in lean-tos (3-sided structures with a floor, but open to the air) even in January or February. In the past, we've recommended a rating of no higher than 20F, but that really isn't enough for our winter camping trips. We recommend a rating of 0F as a good fall-winter-spring bag. For summer camp, you can pack blankets or get a second (cheaper) sleeping bag with a 30-40F rating. Temperatures during summer camp have occasionally dipped into the 40s, but that's rare.

I have two sleeping bags, one has a 15F rating, the other is a 3-bag modular system (military surplus) with a nominal rating of -40F. I don't really think it comes close to that, but it's certainly comfy down below -10F, so long as I have a good ground pad.

References

Sleeping Bags for Backpacking: How to Choose. Long and thorough guide on understanding what you're getting when you buy your sleeping bag. There's more than just temperature ratings involved.

Extract from the EN 13537 european standard. Includes some of the actual text of the EN 13537 standard.

Testing Sleeping Bags According to EN 13537:2002: Details That Make the Difference. Research paper on sleeping bag testing, includes images of the test rig in two postures, including the posture used for \[T_{\rm max}\], the upper limit temperature that doesn't usually appear on sleeping bag ratings.