The materials used for bedding changed in ways similar to those for shelter: from animal hides to woven wool, and from plant matter to linen and cotton cloth, followed by the widespread use of synthetic materials and goose down insulation. At the same time, portable bedding designs progressed from a single rectangular piece of cover to a sleeping bag enclosed at the foot and sides, and finally to the mummy bag design with a hood and tapered foot area for improved conservation of body heat. More recently, sleeping liners of various thicknesses came into use to create a layered effect for maximum warmth, and goose down filling proved its worth by offering excellent insulation and ease of compression for packing. Goose down must be kept dry, however, and is better used in combination with a waterproof bivouac sack—an emergency shelter that is a valuable addition to any pack.
The earliest packs were formed from hide containers or baskets which could be carried in the arms, balanced on the head, or suspended from a shoulder sling. The same sling could be used as a tumpline (strapped across the upper forehead) or breast-strap (across the upper arms and chest) for carrying the load on the back. On the western frontier, items were enclosed in a hide or oilcloth bundle pack, or in a cylindrical roll pack with a sling used in the same manners as above. In the decades that followed, waterproof canvas haversacks or packs became the norm and remained popular until the 1970s, when nylon packs emerged as a lightweight alternative. By this time, backpacks were commonly carried on an external pack frame, which could also accommodate a rolled-up sleeping bag. Later decades saw the more widespread use of internal pack frames, as well as more durable synthetic backpack materials, waist belts, and load-lifting adjustments that allowed more weight to be carried more comfortably.
David Weston Marshall 