For the past many years, we’ve been trying to make sense of temperature ratings for sleeping bags. Our purpose is to assist you in making a wise choice when buying a Sleeping Bag. It is important to understand the function of all features that are built into a bag along with your body condition when using the bag for a comfortable night. By understanding how these features work, you can decide which sleeping bag you need. Features that are useful for colder temperatures may have no place in a summer-weight bag. Bags that are “versatile” may compromise in other areas. Let’s highlight some of the major factors that will guide you to make the right choice.
What do temperature ratings really mean?
The buyer must understand that the ratings given by us or any other manufacturer are conditional. They need to understand all the factors involved in keeping warm. The bag is only an insulator, not a heat generator and we can only estimate the temperature rating of a bag. As a shopper, you must carefully evaluate your own metabolism (the chemical processes necessary for essential body functions) and tolerance of cold. You must decide how much margin to leave for nights you are hungry, wet, sick, injured, exhausted, disheartened, or caught without a tent. In these conditions when a person is not fit may not get a warm sleep even in the high-rated sleeping bag then required one for that place.
FEATURES
Shell and Lining Fabric
The choice of shell fabric and finishing affects the weight, water repellence, comfort, cost, durability, and longevity of a sleeping bag. There is no universal consensus on the best fabric. Often bags will have a tightly woven shell with a DWR (Durable Water Repellent) finish. High thread count fabrics are designed to minimize down leakage and to improve wind resistance. Lighter fabrics may not be as durable or down-proof but careful use may suit your extreme lightweight needs for many years. Cotton is not as strong as nylon and polyester, it absorbs moisture easily, and is hard to dry. Inside liner fabrics are generally lightweight nylon, usually lighter in weight than the shell fabric.
Insulation Materials
The typical insulation materials that are used in sleeping bags include natural fills (down and feathers) and battings of synthetic fibers (hollo fiberfill and polyester fiberfill). These insulating materials are sandwiched between the shell and lining fabrics.
Synthetic insulation is extruded polymers, essentially plastic threads. These threads may be either continuous filament (a single long strand) or short staples, pieces 1.5 to 4 inches long. Either type may be made with hollow threads. The hollow interior reduces weight and traps air for insulation.
Draft Tube
This is an insulated tube running parallel to and alongside the zipper that blocks heat loss through the teeth of the zipper. Otherwise, this area would have a long uninsulated seam running the length of the bag. Depending upon the temperature requirements of the bag, this tube may be thickly insulated, a simple flap of fabric, or absent altogether. For cold weather bags, filled draft tubes may be necessary.
Collar, Draft Collar, Neck Yoke
The collar is an insulated tube covering your throat and shoulders. It may be a flap of fabric or an insulated tube. The purpose of the collar is to prevent heat loss from around the neck. Warm air can be pushed out and cold air sucked in as the volume inside the bag changes. The collar acts as a dam to help slow this loss. Collars are more important in colder weather bags.
Shifting Insulation, Amount of Loft
Down bags may be built with continuous baffles, these are uninterrupted tunnels that run from the top of the bag to the bottom. They allow you to fine-tune the warmth of the bag by redistributing insulation from top to bottom and vice versa. However, continuous baffles can allow down to shift on its own, so periodic shake-ups may be needed. More fill is generally placed into the top of a bag since heat rises and since the insulation value in the bottom of the bag is reduced due to compression.
Sewn-through seams and Baffles
Sewn-through seams are the easiest and lowest cost construction for a sleeping bag. The insulation is sandwiched between the inner liner and the outer shell and the seams sewn through all three layers. “Three” and “four” season Down bags are constructed with sewn-in baffles. In this case, the inner and outer shells are connected by a piece of baffling material that separates the two shells. In that way, the insulation keeps the two shells apart throughout the entire length of the bag.
Hoods
Up to 50% of your body’s heat can be lost through your head, an effective hood is a weight-efficient way of improving a bag’s warmth. Hoods should be able to draw up and close to a 3″ opening, provide room for wearing a hat, and should feel comfortable against the face.
Foot Box
Better-designed mummy bags are flared and boxed and have more insulation in the foot area
Air space within a bag / Cold Spots
Other things being equal, the more snugly a bag fits, the more thermally efficient it is since your body will heat a smaller volume between you and your bag. However, the bag must be roomy enough to allow a good night’s sleep. The amount of space needed is a personal judgment.
Size and Volume of the bag- Length and Width
Sleeping bags with lower internal volume are more efficient since there is less air inside the bag to heat up. First the air inside the bag then the dead air within the insulation must warm up before the bag will begin to insulate. Lower volume bags heat up sooner and insulate sooner.
How to Stay Warm in a Sleeping Bag?
Even during summer nights, cold weather can be expected. In mountainous areas, cold is even more common. Knowing how to properly use a sleeping bag can make the difference between a cold miserable night and a comfortable restful sleep till morning. Keeping warm in a sleeping bag is divided into three main parts; human components, environmental components, and sleep system components.
Remember, your sleeping bag does not produce heat. It is only an insulator that slows heat being lost from your body. In cold conditions, it is important to start the night warm. You will sleep comfortably if you maximize your body’s heat production and minimize heat loss.
- HUMAN COMPONENTS
Role of metabolism and body mass
Taking a short walk or light exercise is a way to increase metabolism by getting your muscles to generate heat. But do not work to the point that you will begin to sweat, this could cause the inside of your bag to become damp.
Diet (protein, carbohydrates, sugar, or hot beverage)
It is important to have enough to eat and drink before going to sleep. Your body will burn fats throughout the night and generate heat. A hot beverage with sugar just before retiring will warm you up so that your bag heats quicker. Sweet food will boost your metabolism and warm your sleeping bag’s insulation.
Age / Physical condition
In general, older people or people in “poor” health will have a lower metabolic rate and therefore, they will have a harder time warming their bag. In this case, they should buy a warmer rated bag.
- SYSTEM COMPONENTS / AUXILIARY PRODUCTS
Your sleep system includes more than just your sleeping bag. Other components that affect your warmth are a sleeping pad, ground cloth, bivy sack, or tent. All of these items will increase your chances of having a warm night’s sleep by reducing the amount of heat lost through convection and conduction.
Ground and ground pad, conductive surfaces
Using a ground pad made with an insulating foam will help prevent conductive heat loss between you and the ground. EVA pad is a major building block of foam and is a good conductor of heat.
Cots, hammocks
The use of a cot or hammock presents a unique situation.
Tent
The use of a tent or bivy bag helps to create another layer of dead air space and helps to reduce convective heat loss.
- CLOTHING
Since the majority of heat is lost from your head, wearing a hat and reasonable extra clothing layers, the more insulation, leading to a warmer sleep solution. The theory that sleeping naked is warmer may be fun, but it is no true.
- HUMAN/ENVIRONMENT INTERACTION
Campsite selection / protection from the elements
Avoid camping in low areas where cold air collects. Moving air causes convective heat losses so campsites should be sheltered from the wind. Be prepared for high elevations to cool quicker when the sun sets or goes behind clouds.
Bag conditioning in the field
It is suggested to open up your sleeping bag as early as you can before sleeping. Giving your bag as much time as possible to fully loft will maximize its insulating value. Pull your bag out of its sack and shake it and fluff it to get air mixed into the insulation. Do this several times before retiring.
Manipulating bag features, adjusting insulation, controlling heat loss
Some models of down bags, for instance, are constructed with continuous baffles. In warmer weather move the insulation to the bottom of the bag and when you find the weather cooler than you expected, move more of the insulation on top of you provided you are using a good sleeping bag.
