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
bedding in situations where a person is sleeping outdoors (e.g. when
camping,
hiking,
hill walking or
climbing). 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 for 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.