Sleeping bags do not provide any heat to keep you warm when it's cold outside. All they can really do is retain the heat your body is able to generate. With this in mind, to stay warm you must do two things well;
1. provide fuel for your body so it can generate the heat you need, and
2. provide a sleeping bag that retains enough of your body's heat to keep you comfortable.
This article will not address fueling your body, but it will discuss the considerations in selecting a sleeping bag that has a good chance of keeping you warm.
Earlier editions of the BSA's FIELDBOOK and several of the books on the OKPIK reading list provide details on making your own sleeping bags, with ratings from Summer to Cold Weather! However, most Scouts will end up buying a commercial bag. If you want to stay warm on a cold night then you need to pick the right sleeping bag. A sleeping bag is one of those places where you can either waste money are not spend enough if you do not know what you are looking for.
There are three major characteristics of sleeping bags: temperature rating, insulation material and construction.
Temperature Ratings
Temperature ratings are made so you can tell what the warmth of the bag is. The rating basically tells what the comfort range of the bag is. If the rating is 20 degrees (Fahrenheit), then you should be comfortable from about 20-40 degrees. But there is one major problem, sleeping bag companies have not set universal guidelines for ratings. Each company places the rating which they feel is correct for their bag. So this causes a little problem for comparing bags.
TIP: If two brands of sleeping bags use the same synthetic insulating material (fill) and have the same temperature rating, it is reasonable to assume that they should have about the same weight of fill (some differences in temperature ratings can be due to draft stops, covering materials and the like). My personal experience is that this is not always the case so be warned! A 0 deg rated bag with 3 lbs of the same fill material as a 0 deg rated bag with 4 lbs of the same fill material is simply not likely to be as warm.
All things being equal, for general 3 season backpacking, a 20 degree bag is the best place to start. This will keep you warm on cold days, but you won’t burn up on hot summer nights.
If you plan on snow camping, you'll probably find that your general pourpose 20 degree bag is not quite up to the Sierra nights! What many experienced hikers end up with is a summer bag rated in the 40 degree range and a 3 season 20 degree bag for all but the coldest outings. For snow camping they'll use both bags, one inside the other, for a combined comfort rating in the 5-10 degree range! This bag-in-a-bag system has the added advantage of minimizing the moisture that frosts up in the bag insualtion. See the BSA's OKPIK Manual for more on this!
| Bag Type |
Comfort Rating (°F) |
| Summer Season |
+35° and higher |
| 3-Season Bag |
+10° to +35° |
| Cold Weather |
-10° to +10° |
| Winter/Extreme |
-10° and lower |
NOTE: You can use low cost bag liners to upgrade a 3-season bag to a cold weather bag! With a liner, you only carry the extra weight when you're going to need it! Common liners are fleece (warmest) and brushed poly/nylon (lightest). Liners also help keep your bag clean on long treks! Now that you know how warm a bag is, don’t you want to know what makes it warm? There are two major material types, down and synthetics. Down is what has been used since sleeping bags were made. This is probably the warmest material for it’s weight and it compacts very nicely in a stuff sack. But if you ever get down wet, be warned, it loses all it’s warmth. This is where synthetics come in. These new materials can be almost as warm as down and can compact almost as much as down. The great thing about synthetics though is that if it gets wet, then it will still be able to provide some insulating value. Synthetics are recommended for all Scout bags because of this. Construction Good quality bags will use an 'offset' construction that minimizes air infiltration through the stiching. Bargin priced bags tend to use the simplier, but less effective 'sewen through' construction. For anything except summer camping, be sure your getting the 'offset' construction! Shape makes a big difference in sleeping bags. The two most common shapes, mummy and rectangular each have their own good points. For anything except summer camping buy a mummy bag. It is called a mummy bag because it is more form fitting and looks like a wrapped mummy. This close shape keeps you warmer since there is less air to warm up inside the bag. The better quality bags will have draft stops at the neck and along the zippers. Be sure you get these features in a snow camping bag! Other Considerations When the ground beneath you has been warmed by the Summer sun, your only other concern may be to smooth out the natural humps and bumps with a sleeping pad. At this point, the choice is one of personal comfort, weight and price. However, for cold weather and especially snow camping, your comfort (and safety when it's really cold!) depend on adequate insulation between you and the cold/frozen ground. On a final note, few sleeping bags are intended for use in wet or windy conditions. That is to say, if the bag is not protected from rain and wind by a tarp, tent, snow cave or some other shelter, the bag temperature rating, and your comfortable night's sleep, goes out the window. So, as a final word of advice, be aware of the weather conditions when and where you are headed and prepare accordingly. This page revised July 22, 2007
Insulation Material
You'll find that the newer sythetics are much lighter and pack much smaller than the older materials of the same temperature rating (assuming similiar manufacturer standards!). However, you'll also pay more for the newer materials. If your planning on more than just causual camping and backpacking, the extra money is worth the savings in weight and size. Dryloft, Polarguard, and Qualofill are the leaders of the synthetic bags. Holfill is an older synthetic that, while a good insulator, lacks the compressibilty of newer materials and should be avoided.
Rectangular bags are usually larger and heavier, though newer semi-rectangular bags minimize these disadvantages. They are not as warm as mummies since they are not form fitting, but offer more room and in general more sleeping comfort. You should consider this type of bag for summer use as the weight issue is minimal and the convenience of a bag that can be laid open on a hot evening is probably worth it.
Even with the highest quality sleeping bags, the insulation beneath you compresses when you lay on it thus losing much of its insulating value. For cold weather/snow camping you need to replace this insulation with a combination of products. As a minimum, a 1 inch thick closed cell foam pad should be used. For snow, plan on using a reflective pad beneath the closed cell pad with a self inflating pad over the two.