In 1917 the zipper was developed and, of course, these made for a terrific seal for the rectangular sleeping bags allowing an individuals body warmth to remain trapped longer consequently keeping them warmer on those cold winter season evenings. Basically the term resting bag essentially suggests a safety bag for someone to rest in.
Rectangle-shaped sleeping bags go as much back as the late 1800's when a mail order catalog pioneer Pryce Pryce-Jones came up with the suggestion to attach 2 rectangular carpets together with ties. He is taken into consideration to be the innovator of today's contemporary rectangular sleeping bag design. After the war he had several of these bags still left as well as made a decision to market them to the public.
Temperature rankings are quite crucial items of details to consider when picking a bag. And although mummy and also rectangle-shaped resting bags can cover a wide range of temperature levels, mummy bags are the common designs for the extreme polar temps such as those you would locate in the Andes.