How to Choose a Sleeping Bag

Sleeping Bag Temperature Ratings Are Only Estimates

Temperature ratings for sleeping bags are only meant to be rough guides. These temperature estimates are often calculated using loft, since the thickness of the bag is something we can measure that has a direct effect on keeping you warm while sleeping.

There are a number of other factors that need to be considered in calculating the warmth of a sleeping bag. These include how well the bag blocks drafts at weak points like the zipper and hood, the method of sewing (layered, sewn through), and the sleeping bag type (rectangular, semi-rectangular, mummy).

Tolerance to Cold Varies

Individuals vary as to how warm they sleep even under ideal conditions. One person may feel very warm in a sleeping bag while the person beside him, in the exact same bag, will feel cold.

In the outdoors or survival situation your ability to stay warm while sleeping is affected by a number of variables related to your body. The quality and amount of food you have been eating has a direct effect on your metabolism and the amount of heat your body will generate at rest. Your physical state after your recent exertions, your level of dehydration

Situations Vary

Other factors of importance in estimating how warm a sleeping bag is include the amount and type of clothing you are wearing. If your clothing is damp, from sweat for example, it's insulation value can be greatly reduced. The quality and thickness of the sleeping pad beneath you is also very important in how warm a sleeping bag will be. Other things that have a bearing in sleeping bag warmth include the shelter you are in, the amount of wind and humidity.

When buying a sleeping bag ask yourself this: "What are the Conditions in Which I Will Use my sleeping bag?"

Sleeping Bag Temperature Range

When selecting a sleeping bag, we often consider a temperature range related to the environment we are likely to find ourselves. Using a temperature range in sleeping bag selection allows for a margin of safety for the reasons we discussed above.

Rough estimates for temperatures related to season and use in mountainous may be something like the following, though of course this will depend upon where you are located:

Summer Camping. 35 to 50 degrees F
Spring and Fall 15 to 30 degrees F
Winter -30 to 0 degrees F
Mountaineering, Arctic -60 to -10 degrees F

Sleeping Bag Shapes

Mummy sleeping bags are the most efficient due to their tapered shape. This allows the use of the least amount of material, thereby reducing weight and bulk. In addition, a mummy sleeping bag minimizes the amount of dead air space inside the bag that your body has to heat.

A problem with using a mummy sleeping bag is many people find them too restrictive.

Rectangular sleeping bags are the least efficient sleeping bags. They require more material and have the most extra space inside that your body must heat in order to stay warm. However, the extra space is welcomed by people who feel claustrophobic in a mummy sleeping bag. Many people feel the extra weight and bulk is offset by the bags roominess and more comfortable sleep. In the wilderness or survival situation, sleeping well is of paramount importance.

Semi-rectangular sleeping bags are a compromise between the mummy and rectangular shapes. A semi rectangular bag offers more room than a mummy bag and less bulk, weight, and air space to be heated than a rectangular bag. Many people choose semi-rectangular sleeping bags.

Size of Sleeping Bag

The length of a sleeping bag is calculated from the toe to the neck and does not include the hood. Be sure to add a few inches to your height in order assure enough room in the bag to be comfortable. Any extra length needs to be heated by your body so do not choose a sleeping bag that is too long.

Especially in cold weather, you may need a few inches at the bottom of the sleeping bag to place your clothes for the next day, boots, water container, etc in order to keep them warm or from freezing.

Insulation Material

The type of sleeping bag insulation has a direct effect on how warm it is.

Under ideal conditions the best sleeping bag fill is down. Of the types of sleeping bag fill down is usually the most expensive. The big problem with down sleeping bags is that if the down becomes wet it's value as insulation is very poor. In many outdoor and survival situations this makes depending upon down sleeping bags risky.

Synthetic fill for sleeping bags includes products like Polarguard, Primaloft, Thermlite and Lamolite. Manufacturers make bold claims as to why their particular fill for sleeping bags is the best. In my experience, Primaloft is an excellent choice if you are using your sleeping bag in damp or wet conditions. Wiggies Bags uses an insulation they call Lamolite which I have found to have excellent performance under a variety of adverse conditions.

Down bags sometimes use fill ratings to describe the amount of loft per unit of weight the sleeping bag has. A fill rating of 700 means that one ounce of down fill will expand to 700 cubic inches. A fill rating of 800 would mean the bag can be made a bit lighter for the same temperature rating since less fill by weight is necessary in order to create the same amount of sleeping bag loft. The higher the fill rating of a sleeping bag the lighter it will be and less bulky when compressed.

Sleeping Bag Features

Your head and neck hemorrhages heat, by some estimates 20 to 25 percent of the heat your body loses is from this area. When choosing a sleeping bag a well insulated hood with drawstring is very important. Multi sectioned hoods, created using multiple panels of insulation creates a better fit than single panel sleeping bag hoods.

An insulated draft color around your neck with drawstring closure works to keep air from circulating in and out of the bag via the neck area.

A draft tube is important because it runs the length of the zipper, blocking cold air will try and enter via the sleeping bag zipper.

Velcro closure tabs at the top of zippers and somewhere along draft tubes insures that these do not come undone while sleeping.

Staggered seams and insulation in layers prevents cold spots by preventing the seams from lining up with the outer sleeping bag shell.

Sleeping Bag Care

The care a bag requires is an important consideration when choosing a sleeping bag. Down requires the most care and synthetics the least. Dry cleaning a down sleeping bag is a higher requirement than carefully cleaning a synthetic sleeping bag in your bathtub.

When storing, do not compress your sleeping bag or long periods. This could result in loss of of loft when you are using it. Store a sleeping bag in a large breathable container so that it retains its loft.

Use a sleeping bag liner. The liner will prevent body oils from penetrating and lessening the value of the sleeping bags insulation.

How to Stay Warm in a Sleeping Bag

Before getting into your sleeping bag, loft it up by shaking gently. The loftier you can get the insulation your bag, the warmer it will be.

Staying dry is number one since the insulative value of the fill decreases with dampness. Dry yourself off as much as possible before entering the bag and do not place damp clothing inside with you. Avoid breathing into your snug cocoon because this causes condensation.

A good thick sleeping pad is very important. Much of your body heat is lost through to the ground. The sleeping bag insulation beneath you is compressed by your body weight and so is nearly useless. Your pad is what insulates the bottom portion of your sleep system.

Wear some warm, dry clothes to bed. Sleep clothing will retain heat even closer to your body, and help keep your sleeping bag dry and clean.

Wear a warm hat in your sleeping bag in order to retain heat next to your skin.

Be sure to help keep your body in excellent physical condition by eating plenty of nutritious and calorie laden food. Drink more water than you feel you need. Your body is an furnace and can only produce heat if you supply it with the amount and type of fuel it needs.