Sleeping in the backcountry is supposed to be roughing it, but the difference between roughing it and being miserable and roughing it and loving it is as simple as a comfortable sleeping bag.
Sleeping Bag Styles
The difference in sleeping bags is readily apparent. Two main styles are on the market, mummy and rectangular.
Rectangular bags allow you to move around more, and are great for those "toss-and-turn" sleepers. However, this additional room comes at the price of additional weight and potential heat loss. The rectangular design does not pack well and is better suited for a car camper, or if you have additional pack equipment such as horses or ATVs to get your gear to camp.
Double bags are actually a combination of two rectangular bags that zip together, or designed as one large, two-person bag. Truly a car camper, these bags are not designed for packability but more for family camping comfort. A nice benefit of double bags is that they often have different insulation levels in the top and bottom layers, giving you two different bags when used separately.
Mummy bags received their name because of their tapered shape, looking much like mummies from an Egyptian tomb. While they are not as roomy, mummy sleeping bags weigh 1% to 20% less than rectangular bags of the same temperature rating. They also pack much smaller. Mummy bags are favored among backpackers who have to carry their camp on their back, and need to make every ounce count. In addition to being small and lightweight, Mummy bags are also more efficient at insulating you from the cold. They have less dead air space to heat, and most bags incorporate an insulated hood and neck collar that can be drawn snug as the temperature drops, preventing heat loss through the largest source, your head.
Many different insulation types are on the market. However, the two main types are synthetic (manmade) fibers and down (primarily goose feathers). They each have their benefits, and at times, a combination of the two creates the best option.
Made from the undercoating feathers of geese, this soft material is an exceptional natural insulator. The secret to its warmth is the loft it provides, trapping air as an insulator. This is also how it is measured — with a number indicating a volume of air that is displaced by one ounce of down. For quality down, look for fill-power values of 600 and greater. This higher loft number indicates a higher purity down that will loft greater when unpacked and provide more warmth.
Down is also a very light material for the warmth it provides, and is extremely compressible - allowing you to pack a large, warm bag in a very little space. The drawback with down is that it loses its insulation value once it becomes wet. Since it takes a long time to dry in the field, this is a concern if you use the bag in wet conditions. With a down bag, also look for construction that prevents the down from shifting and bunching up, possibly forming cold spots.
Most synthetic insulations are constructed of a long hollow-core fiber that is layered to trap air and provide insulation. The hollow-core fibers are lightweight and have numerous air pockets for better insulating capability. With a synthetic bag, it is a good idea to look for multiple layers that are offset or overlapping. This prevents cold spots and blocks air from moving from one layer to another.
Synthetic materials are usually heavier and bulkier than down, and they are not as compressible. That does not mean that they are not for backpackers though. Unlike down, synthetics do not lose their insulating ability when they become wet. Should they become wet, they absorb very little water and dry quickly, making drying in the field a possibility with a little heat or sunlight. Price is always a consideration, and compared to a quality down bag, a synthetic model will be less expensive.
Size and Weight
In explaining style and insulation, we’ve already touched on a lot of this. If space or weight is of utmost concern, a down mummy bag is the best choice. It is all a matter of how and when you will use your bag. Look at the various ratings and carry weights to determine what is best for you. Sometimes the best answer is two bags — a compact model for backpack trips and a larger rectangular model for comfortable sleeping on a cot at base camp.
The other factor to look at is length. Commonly, sleeping bags come in two lengths, regular and long. Generally, if you are six feet tall and under, a regular length bag will be more than adequate. However, if you are over six feet tall, you may want to look at a long bag for extra comfort.
Outer Shell Material
Depending on the use of your bag, you may want to look at the outer shell material. If rugged field use is in your plans, you want a shell material that can stand up to it. Heavy cotton canvas works well for rectangular outfitter bags, but with its weight and stiffness, it doesn’t suit a packable bag. Synthetic material such as ripstop nylon or Pertex is a better choice for increased packability, while still maintaining excellent durability.
If you plan to sleep outside with your bag, you will want a shell that is at least water-resistant, to protect you and your bag from light moisture. With all the stitch lines in a bag, it is hard to make it completely waterproof. If sleeping outside in inclement weather is in your plans, a weatherproof bivy sack or shelter is your best option.
This is the main measuring stick used to differentiate between bags. Bags all differ in fill weight, fill type, size and style, but every one has a temperature rating on the tag. What does that mean to you?
The temperature rating is derived as the lowest temperature that the average person can tolerate and still remain comfortable within the bag. Most manufacturers try to maintain similar methods in establishing temperature ratings, but you should know that no standard has been fully accepted industry wide. Therefore, variances do exist from manufacturer to manufacturer.
The other variance that exists is "the people factor." I mentioned it above and it is for the average person. When speaking about thermal comfort, it is hard to find an average person. Rarely will you find two people in the same room that agree on a temperature that is right. A good example is in our office space; whenever I think it is finally cool enough, others are turning on their space heaters because they are too cold.
Selecting a Comfort Rating
Before selecting a rating, first determine the coldest temperature at which you will be using the sleeping bag. Remember that this is only an estimate. You can’t always predict what the weather will be on next week’s camping trip, but you need to start somewhere. Also, women tend to be a bit more sensitive to the cold than men, so women should usually try to err on the colder side with their estimate. It is also a big help to know how you view temperatures in regard to other people. I usually run a bit hotter than the rest of the crowd, and most temperature ratings for bags seem to be right on for me.
If you camp in warmer conditions than your bag’s rating, you will have to ventilate it slightly. Most incorporate two-way zippers that allow you to zip up and still ventilate portions of the bag, especially the footbox, to release the excess heat. If it is really warm, you can also leave the bag unzipped, and you will definitely want to loosen all the drawstrings on mummy bags.
Can I Pick One that is Too Hot?
That one is simple – YES! Picking a bag that is too warm will cause you misery in the long run. Whether at home or camp, I always sleep better if I can remain under the covers. If you pick too warm of a bag, you will be forced to endure a long night alternately sweating and freezing as you throw the top layer back and forth.
When I first started backpacking in college, one guy I hung out with always had the most extreme gear, stating that "you never know what will happen." So, preparing for the worst, he obtained a minus 30° bag. The hole in his theory was that most of our camping was under summer conditions and temperatures never dipped below 40°. His bag turned into an expensive sleeping pad since he was forced to sleep on top of it every night.
For me, a 15° bag is just right for all my three-season camping needs. I can vary what I wear to bed and adjust the zippers and hood drawstrings to make it fit nearly every situation. I have only been cold in the harshest winter conditions where the temperatures approached 15°. If you plan on camping in all four seasons, the best solution is to purchase two separate bags. Pick up a heavy winter bag for the cold times, and then use a lighter, three-season model for the rest.
Some Other Things to Think About
When searching for your sleeping bag, there are several other questions to ask to help refine your bag selection.
Sleeping on the ground? — Conduction will quickly cause you to lose body heat and feel colder than the temperature dictates. A good solution is to always sleep on a sleeping pad or air mattress, providing a layer of insulation from the cold ground. If you sleep on a fabric cot, a thin pad is also a good idea to prevent cold air from circulating under the cot, robbing you of precious body heat.
Do you mummy up? — Most mummy bags are configured with a narrower profile and a hood, the theory being it is easier to heat a smaller space. To achieve the published temperature rating, most manufacturers count on you remaining fully zipped up and having the draw cords for the hood and chest collars pulled tight. Some people do not like this cozy feeling and actually feel a bit claustrophobic, refusing to draw the hood tight. That is fine, but then your head acts as a giant radiator and pumps out a lot of body heat.
If you get a little claustrophobic, you may want to look for a warmer bag to compensate for the additional heat loss. If you are still against mummy bags, another solution is a light fleece hat to wear to bed, preventing the major heat loss from your head.
What do you wear to bed? — Simply by changing your clothes, you can easily vary the temperature of the bag. A layer of quality thermal underwear and heavy socks can extend your comfort zone by up to 15°.
Do you sleep in a tent? — Sleeping in a tent is much warmer than sleeping outside. Your radiated body heat will slowly warm the microclimate inside the tent. You will really notice the difference in smaller, backpacking-style tents, since there is less air to heat. If only a couple people sleep in a huge, family-size tent, most of this radiated heat will be lost.