A sleeping bag is an insulated covering for a person, essentially a lightweight quilt that can be closed with a zipper or similar means to form a tube, which functions as lightweight, portable bedding in situations where a person is sleeping outdoors (e.g. when camping, hiking, hill walking or climbing). It is also commonly used indoors for people who do not have beds or at sleepovers. Its primary purpose is to provide warmth and thermal insulation through its synthetic or down insulation. It also typically has a water-resistant or water-repellent cover that protects, to some extent, against wind chill and light precipitation, but a tent is usually used in addition to a sleeping bag, as it performs those functions better. The bottom surface also provides some cushioning, but a sleeping pad or camp cot is usually used in addition to that purpose. The bottom surface of a sleeping bag may be moderately water repellent, but a plastic tarp or groundsheet is often used to protect against moist ground. There are a range of sleeping bag models designed for different purposes. Very lightly insulated sleeping bags are designed for summer camping use or indoor use by children during slumber parties. Well-insulated bags are designed for cold weather use. The most well-insulated and lightweight sleeping bags, which are designed for serious hikers and adventurers, are more expensive than lightly insulated sleeping bags. One subcategory of cold-weather sleeping bags, the mummy bag, is so named because it has an insulated hood for the head. A bivouac sack (bivy) is a waterproof cover for a sleeping bag that may be used in place of a tent by minimalist, experienced hikers. A bivy bag may also be carried by day hikers as a backup or emergency shelter, to be used if they cannot make it back to their starting point by nightfall due to inclement weather or getting lost.
History
In the 1850s, Elverys Sports in Ireland marketed a proto-sleeping bag known as the Crimea Wrapper towards soldiers being posted to the Crimean War. The "Euklisia Rug", from Ancient Greek εὖ (well) and κλισία (cot, sleeping-place), patented by mail-order pioneer Pryce Pryce-Jones in 1876, was also a forerunner of the modern sleeping bag. Pryce-Jones, a Newtown, Montgomeryshire, Welsh entrepreneur developed the bag and exported it around the world in the late 19th century. Documents show he sold 60,000 of these rugs to the Russian army – and the British Army also bought them. There are records of civilian uses among missionaries in Africa and pioneers in the Australian outback.
Design types
A basic sleeping bag is simply a square blanket or quilt, fitted with a zipper on two or three sides, which enables users to get into the bag and then close it up. A sleeping bag of this type is packed by being folded in half or thirds, rolled up, and bound with straps or cords with cord locks. The basic design works well for most camping needs but is inadequate under more demanding circumstances.
The second major type of sleeping bag, sometimes called a mummy bag because of its shape, is different in several important ways. It tapers from the head end to the foot end, reducing its volume and surface area, and improving its overall heat retention properties. Some bags are designed especially to accommodate women's body shapes. Most mummy bags do not unzip to the feet, because the zipper is a weak point in any sleeping bag's insulating qualities. Together with the tapered shape, this design feature helps protect the feet, which are more vulnerable to heat loss than other parts of the body. Another design feature is a drawstring, equipped with a cord lock, at the head end to help prevent the escape of warm air. A mummy bag often cannot be rolled neatly like a rectangular bag. Instead, it is simply stuffed into a stuff sack or compression sack. The bottom of a sleeping bag typically does not provide significant insulation, because body weight crushes the loft of the insulation material. It is therefore necessary to use a pad or other less crushable insulation underneath the sleeper, especially in cold weather. Due to this, some sleeping bags do not include insulation on the bottom. Some include a sleeve for holding a sleeping pad. Additionally, some campers, especially ultralight backpackers or hammock campers, have started to use a top quilt, essentially a sleeping bag without a back. Some top quilts include a foot box, while others are just simple blankets.
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