The primary function of a sleeping bag is to keep you warm. As such, it is an excellent insulated envelope/cocoon-like heat-retention chamber in which to sleep. Factors to consider when choosing the proper sleeping bag are directly related to: temperature, weight vs. warmth and insulation.
Casual home or backyard and light car campers require minimal sleeping bags. For general family camping, car/tent use, the traditional rectangular bag is common. Cabin or hunting/fishing camp sleepers might prefer the heavier, warmer rectangular bags while backpackers and other lightweight campers usually prefer the benefits and warmth of lightweight down. Extreme polar conditions require expedition quality winter bags.
At the foundation of the mechanical factors regarding levels of comfort/warmth in a sleeping bag are the human elements of a body’s metabolism (producing heat), blood circulation (distributing heat), gender (women tend to be colder than men), and hydration (we tend to stay warmer when we are adequately hydrated). These human factors will determine at which temperatures we feel the most comfortably “warm.” That personal sense of warmth can be used to determine which sleeping bag might best provide that comfort zone while sleeping.
Generally then, the following construction features all combine to provide a range of temperatures at which each bag should provide an accepted range of comfort. Summer/Indoor bags are best suited for temperatures above 40 degrees F; general 3-season bags range between 10 degrees F and 40 degrees F; winter campers should consider bags within a –10 degrees F to +10 degrees F. In the most extremely low temperature ranges, bags should be rated even lower!
A new standardized rating system for sleeping bags has been introduced from Europe called the European Norm (EN) 13537 Protocol that sets comfort limits for both Men’s and Women’s sleeping bags (remember, women are typically colder than men):
* Upper EN Limit: the highest temperature at which the average man can sleep comfortably;
* Comfort EN: the lowest air temperature at which the average woman can sleep comfortably;
* Lower EN Limit: the lowest air temperature at which the average man can sleep comfortably.
* Extreme EN: the “worst case scenario” rating — a bag designed to keep a woman alive!
Your safest bet in determining the proper sleeping bag temperature range is to decide on the coldest temperature you expect to encounter and pick a bag with a low-end rating of about 10 degrees colder.
Here are a few basic terms that are used to describe function, materials and uses of most sleeping bags:
Insulation doesn’t provide warmth by itself but is the material used to create the barrier of trapped, non-circulating “dead” air that retains our body heat. Bags are filled with either natural (down, duck), synthetic insulation and in some cases simply cotton.
Weight is a primary factor when choosing a bag for backpacking or personal carry beyond a vehicle. Most often the main factor in a sleeping bag’s weight is the amount and type of fill. The shape of the bag can also affect the overall weight.
This represents the amount (height/thickness) of fill in a sleeping bag. The higher the loft (which helps form air pockets), usually the warmer the sleeping bag. And when comparing the same type of fill, more loft typically means more weight and more warmth. Therefore the amount of trapped heat (warmth) relative to the amount of fill (weight) equals the warmth/weight ratio of a sleeping bag.
The outer, exposed cover, the “skin” of the sleeping bag. Shells are commonly made of synthetic fabric (taffeta or ripstop nylon, polyester) and are often treated with a durable water-resistant (DWR) finish. Some inexpensive/summer bags shells are made of heavier cotton.
A lining is the inner surface that makes contact with the sleeper’s body. Linings can be silk, cotton flannel, fleece, insulated fiber or other or other synthetic materials. These general features, and others, are incorporated into a sleeping bag’s design to offer a range of function in the different types of sleep systems. “Liner” is also the term used for a separate, interior bag added to a sleeping bag (see below).
Shapes Of Sleeping Bags
When we are in a sleeping bag the heat from our body warms the pockets of air that envelops us inside the bag. That warming process is more efficient and effective when that “dead” air between our body as well as the air trapped in the sleeping bag insulation doesn’t move around a lot or fill too large of a space. A good-fitting sleeping bag will envelop the body in a warm but not excessive pocket of dead air. This is why mummy style bags are warmer than the larger, more spacious rectangular bag designs.
The common flat, envelope-shaped sleeping bag most of us grew up using as kids. It features a common width from head to toe and can vary in length and width, but retains its rectangular shape. This is a popular summer bag shape, and well suited for backyards and car-camping. Its roomier shape enables the user to move around more freely within the bag. Some rectangular bags are for cold weather use (base camps, winter cabins, etc.) and tend to be heavier bags.
A common backpacking style, its “mummy” shape most closely follows the general form of the human body: rounded at the head, broadening outward at the shoulders (and a bit at the hips for women’s bags) and then tapering back downward to the feet. This design allows for more restrictive inner bag movement, but does enable the entire bag to move in unison with its occupant. Colder weather bags and mostly all down-filled bags incorporate the mummy design. Mummy bags tend to be the lightest yet warmest style of sleeping bag.
Semi-rectangular or modified Mummy/FootBox
This bag has the general appearance and shape of a standard mummy design, but features an enlarged, often squared off, box-like area at the foot of the bag. This style of bag is midway between the two designs in shape, but much more closely aligned with a standard mummy bag in function and use.
Men’s vs. Women’s Sleeping bags
Particularly within the mummy/semi-rec’ bag arena, bags designed for women tend to be shorter, have narrower shoulder widths and wider hip widths. Women also tend to be colder than men so a woman’s bags may have more fill designed into the torso area of the sleeping bag.
All About Fill/Insulation
The “stuffing” inside a sleeping bag is either natural down (goose or duck) or one of many, often proprietary per manufacturer, synthetic fibers. And the least expensive bags use cotton. Filling is judged on its ability to insulate relative to the amount of air trapped within the spaces between the fibers that help maintain warmth within the bag. The amount of the filling is also the major factor in determining the bag’s weight.
The gold standard of sleeping bag insulation, down is the lightest, most compressible, durable (tends to hold up longer than synthetic fibers) and most efficient insulation you can get. It is the tufts of feathers that grow as an undercoating on geese and ducks. It is superior for keeping a person warm in cold, dry conditions. The effectiveness of down uses a rating system from about 600 to 900 that represents the volume in cubic inches of space 1 ounce of down will fill. The higher the number, the more space, and thus the more insulation ability (warmth) for the same amount of fill weight. Conversely, the same temperature rating of a down bag will make an 800 down bag lighter in weight than a 600 down rating because it takes less down to achieve that comfort level. Goose down tends to retain its lofting ability longer than duck and is slightly more expensive.
A critical limiting factor in down is its total loss of insulating affect when it’s wet! If there’s any chance your sleeping bag will be exposed to unavoidable moisture, you should consider down treated with a water resistant application or a bag filled with synthetic insulation.
Made of polyester fibers, synthetic bags will keep you warm even when wet, are quick drying and non-allergenic (unlike down). Synthetic fill doesn’t compress quite as much as down and tends to wear down faster over time. Some manufacturers use hollow fibers, others coat the fiber with silicon. Many proprietary treatments exist throughout the sleeping bag industry.
Polyester fibers are made into short strands and then densely packed. This process minimized heat loss and gives the synthetic bag a “down” feel and excellent compressibility.
Uses a strong and durable filament that also adds loft. These bags may not compress as much as those using short-staple fill.
These fills are arranged throughout the sleeping bag by the use of chambers called baffles (down), shingles and quilting (synthetic). Some bags have inner walled compartments sewn in that are filled with insulation; others use baffle tubes or shingles of fill arranged and sewn together to keep the fill from bunching up or shifting around within the shell. Some bags use a layer of insulated quilting to provide warmth. Besides the amount and type of fill being used, the method used to secure the insulation in place plays an important role in insulation and warmth.
- Sewn-through/stitch-through: used on bags with low volumes of fill (no baffling). Stitching that pulls the shell and lining close together can create cold spots along that seam. Often used in down bags.
- Box Baffles: basically a four-sided chamber, with straight or slanted sides or trapezoidal in shape. Some box baffles are stacked in two layers, offset at the seams like laying bricks in a wall.
- Shingle Baffles: attached to the shell and the lining, these sheets or sections of insulation overlap like the shingles on a roof. A modified shingle baffle, called “Wave construction” uses a shingle longer than the space length forcing the sheet of shingle to compress into a wave formation.
- Continuous Baffles: wraps the insulation around the entire bag allowing for shifting a portion of the insulation from the top to the bottom based on seasonal temperatures.
- Side Block Baffles: another seasonal adjustment that enables user to shift insulation from torso to lower body.
- V-tube Baffles: “V” or triangular-shaped baffles are used to keep down from shifting. Slightly heavier due to number of baffle walls throughout bag.
- Offset Quilting: features offset stitching of layers of insulation panels. In inexpensive, warm weather bags, the shell, the quilted layer and the lining are all stitched together and as such are prone to cold spotting along those seams.
- Other construction methods: differential cuts create a sleeping bag where the outer shell is slightly larger than the inner liner. Differential fill means more insulation is on top rather than on the bottom of the bag. Some manufactures also use welding to fuse the baffling to the shell and liner thereby eliminating all puncture breaches to those surfaces.
Components & Features
Once these basic construction/design factors are taken into consideration, there remain other components and features of a sleep system that can affect comfort and function. Here are some important ones:
While a standard feature, consider length options: Partial zippers usually run full body, but end somewhere in the lower torso/upper leg region. Some partial zippered bags offer vented foot panels to provide ventilation in the non-zippered portion of the sleeping bag. Full zippers go the entire length of the bag and completely around the bottom, thereby enabling the bag to be fully opened and used as a comforter type cover. You can choose right or left-handed zipper positions (when lying on your back). Opposite zippers enable two bags to be zipped together to form one large bag or to split warmth side by side. In selecting this combination, make sure zippers are the same size and relative strength/stoutness. A stiff backing will keep zippers from snagging.
An alternative to a side zipper is a center zipper that opens down the middle of the bag. This enables the user to sit up, partially enclosed in the bag but with the use of arms and hands.
This is a long, insulation-filled baffle tube that runs along the entire inside of the zipper preventing drafts, or cold touch from the exposed zipper teeth.
Standard in mummy style, other bags often utilize a cinch hood that conforms snuggly around the head for added protection against the cold and drafts.
A tube/flap at the neck opening (collar) or a horseshoe-shaped baffle (yoke) at the neck-shoulder area to prevent heat from escaping and cold air from entering the bag.
Sewn into the head area of the bag, a pillow pocket enables user to stuff a camp pillow or soft clothing behind the head area within the sleeping bag. Smaller pockets are sometimes attached to the upper, outer shell of the sleeping bag for small accessory items (glasses, cell phone, flashlight, etc.).
An enlarged, box-shaped foot area with side panels of insulation giving the sleeper more space at the bottom of the bag.
Some bags have a sleeve incorporated into the bottom of the bag to insert a sleeping pad. Such pads add a degree of comfort, insulation to the bag, and of course, keep the sleeper from sliding off onto the tent floor or ground. Straps also enable a pad to be secured to the bottom of the bag.
Sleeping Bag Liner
An inner bag liner separates itself from the bag lining itself. Offered in silk, fleece, flannel, or regular cotton, this liner keeps the interior of your bag clean as well as adding up to 15 degrees of warmth depending upon the material and conditions. It can be easily and frequently removed and washed.
A Bivy Sac is an outer tent-like cocoon, usually with a heavier floor that serves to protect the sleeping bag from the elements as does a tent, but without the structure.
Similar to a bivy sac, but lighter, but it also extends the range and protection of the sleeping bag.
The “comfort” range of temperatures given for a sleeping bag is generally based upon the sleeper wearing moisture-wicking undergarments, wool socks and some type of hat.
- Use of a bag liner, as mentioned above, helps keep you warmer and the bag cleaner;
- Upon arrival, open out your sleeping bag as soon as possible to allow the loft to expand to its fullest before sleeping;
- Waterproof ground cloths or pads will keep the bottom of the bag dry;
- It is best NOT to sleep in the same clothing you’ve been wearing all day;
- Stuff a bag feet first and with the zipper partially open to better enable air to escape;
- Air out a sleeping bag — inside out — daily if possible, but absolutely after each trip;
- Never store your sleeping bag for an extended time in its stuff sack, use a larger, storage bag — and make sure the bag is completely dry.
- Perhaps consider having two sleeping bags; a slightly oversized/larger lightweight “summer” bag and your normal size for a “3-season” bag. Each can be used alone, or combined (3-season inside the summer bag) to extend its use into lower temperature ranges for extended seasonal use and extra toasty comfort.
- Maintenance Tips
It is always best to follow the manufacturer’s instructions for any cleaning of a sleeping bag. For small, soiled shell areas, typically a toothbrush and a mild detergent paste will work. When gently scrubbing, pinch the shell and lift the fabric up from being in contact with the interior insulation
Generally, a full wash in a machine requires specific steps for preventing damage to a bag. A waterlogged sleeping bag is incredibly heavy. Front-end washers are gentler than top-loaders. Once you’ve washed and rinsed the bag according to instructions, Let as much water drain out of the bag as possible and then, from below, cradle as much of the bag as possible when handing it to dry. Always hang a wet bag lengthwise from head to toe. Unless cautioned against by the manufacturer, you can usually toss a sleeping bag in a commercial drier set on low heat or air dry to finish drying and regain loft. Adding a soft but firm item (small gym shoe, tennis balls, etc.) will help break up any bunches of insulation that might have formed during the washing process.
Selecting the right bag is a serious undertaking. If you are able, try the bag out first — wear clothing of similar bulk that you’ll wear while sleeping. Use a pad if the bag has attachments to make sure you still have adequate room and comfort, and check the “fit” to satisfy your own squirming maneuvers.
A comfortable night’s sleep is a critical factor in the success of any camping trip. Today’s sleeping systems, using space-age materials and applications, are being created to optimize warmth with minimal weight — and at affordable pricing. Take the time to check out all your sleeping bag options, your good night’s rest is going to depend on it.
Good luck picking out your sleeping bag and enjoy your time in the Great Outdoors! Be sure to visit Sportsman’s Guide for the latest sleeping bags.