Sleeping
Bags
A sleeping bag is a protective "bag" for a person to sleep in, essentially a blanket that can be closed with a zipper, velcro, or buttons, and functions as a bed in situations where it is impractical to carry around a full bed.
Its primary purpose is to provide warmth and thermal insulation. It also protects, to some extent, against wind chill, precipitation. The bottom surface also provides some cushioning, but a sleeping pad is usually used in addition for that purpose.
A bivouac sack, or poncho can be used as waterproof cover for a sleeping bag that may be used in place of a tent for lightweight travelers or as a backup if inclement weather occurs.