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.
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.
Remember that with time, from typical use, a treking sleeping bag will certainly lose its warming performance. This results from the fill obtaining a bit much more compressed. This will cause the "air pockets" to go away.