A sleeping bag is a protective bag, analogous to a bed and blanket. A person enters into this bag and uses it like a bedding whenever he/she wants to sleep. A sleeping bag in other words is a square blanket that is fitted with a zipper on the three sides with an opening on one side. The lower surface of the bag is filled with soft materials to provide a cushioning effect to the sleeper. The bag cover is made of bivouac, a waterproof material that protects the sleeper from rain and wind. The bag is most useful whenever the traveler is unable to fix a tent because of inclement weather.

Functions of a sleeping bag

The primary function of such bags is to provide warmth and insulation to the person sleeping inside it by regulating the temperature. A bag therefore comes with a minimum and maximum temperature rating, which can be adjusted according to the need of the occupant as comfort for one person varies with another.

The degree to which insulation occurs depends primarily on the insulating material used. The other conditions for proper insulation are the way the bag is constructed and the amount of loft present in the bag. Goose or Duck Down is the commonly used insulating material. This material is light, compressible and the best known natural insulator available. Using them allows for folding the bag into small pack, which can be carried as a backpack by the traveler. Down however costs more and is best suited for drier conditions. In wet conditions the Down needs greater care. So some manufacturers use synthetic fill to lengthen the life of the bag and also to keep its price low.

Synthetic fill comprises of small fibers that are treated with silicon to increase the loft. One of the physical features of fibers is that they contain chambers that are capable of trapping air. Although these synthetic fibers are closer to natural fiber efficiency, they are however, not on par with natural fibers. But the advantage of these fibers is that, they can be used in all sorts of climate and by people who are allergic to Down. These advantages make these synthetic fibers the preferred type of filling by many journeymen.

The other materials used in the preparation of bedbags are cotton and wool. Wool although is good at repelling water because of its natural greasiness, weighs much more than any other type of filling. Another problem with wool is that it resists compression. Cotton on the other hand, retains water and so adds to its weight. However when compared cost wise, this material costs less and also can be molded into various different designs. Therefore the sleeping bag prepared from this material is very useful in stationery camping, where weight hardly matters.

Types of bed bags

Many varieties of bed bags are available in the market. The user can choose the one that suits best his/her

sleeping habits and the external environment like the temperature, ruggedness of the land and climate where he/she is going to camp, as sleeping in a bag will compress the bag reducing the air space and the bag insulating capabilities. Choosing a bag also depends on how he/she is going to carry the pack, that is whether on the back or in a canoe or through some other mode of transport.

Various shapes of bed bags

A traveler can choose bed bags of three basic shapes rectangular, cocoon or mummy and tapered shape. A rectangular shaped bag is large and hence offers enough space inside. This type of bag is available in single and double size. A double sized bag is large enough for two people of average size to sleep in.

The Cocoon or mummy shaped bag is of another type. These bags are in a cocooned shape which appear like Egyptian mummy, hence are called mummy bag. The bag is divided into three portions - the middle portion is of normal shape, but the two end portions are narrower as the bag tapers at both the ends. Because of this tapering, the volume and surface area of the bag reduces to a considerable extent. However, the advantage of such a shape is that it improves the bag overall heat retention properties especially near the foot and head (some bags even have hoods near the head) from where there are more chances of heat being lost from the body. Another advantage is that, this shape also provides a cozy feeling to the person sleeping inside. However the basic disadvantage of this shaped bag is that it cannot be rolled or folded like a rectangular bag, but can only be stuffed into a stuff sack or compression sack.

The third shape in which a sleeping bag is available is the tapered shape. This shaped bag is wider in the area, where the sleeper shoulder comes and tapers down at the bottom or near the feet. It also functions similar to cocoon shaped bag, but is more useful to men because of its shape.

Sizes

The bed bags are commonly available in junior or the youth size and the adult size. They are all available in regular sizes but sometimes are also provided with extra-long and extra-wide facilities. These extra spaces are required to store some necessary things like boot, drinking water, flashlight, batteries, etc. in the bag during the night. These things although seem paltry, are very essential while trekking.

A sleeping bag may not in reality replace a bed at home in all aspects, but it surely can become an alternative, comfortable sleeping location for people who are camping out on their journey.