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I have never used a Mummy type sleeping bag, rather I have hardly used a sleeping bag. I am afraid, I am more of a carry-mat, sleeping-pad and a blanket guy.

It never occurred to my mind that What must be the advantage of a Mummy type sleeping bag over a Blanket type? over even vice-versa if it is so?

{ asked by WedaPashi }


Basically it boils down to "less weight for the same insulation" in favour of the mummy type for two reasons:

In a blanket type bag you have more or less two insulating sheets, one on top and one below your body. For a mummy type maybe a bit more than the area of one of those sheets would be enough to wrap your whole body. This already reduces weight and pack size.

Above that, a mummy type bag wraps your body quite closely, therefore leaving only a small air volume that has to be warmed up. The blanket type has way more "dead volume" that you have to heat and keep warm with your body's heat. To get the same insulation, a blanket bag needs more loft material, which makes it heavier and bulkier.

Both factors might be not of great importance in warm climates where you don't need high insulation but only something to cover your body at night. As you get to climates where the sleeping bag is necessary to prevent hypothermia, a blanket type bag that provides the insulation needed will soon be way to heavy and bulky.

Just as a side note: if you go to very cold climates (winter mountaineering, arctic tours), everything is done to prevent heat loss, therefore some of the bags designed for those climates have only a half length zipper or even no zipper at all to prevent cold bridges.

TL;DR: Whenever it gets cold enough that insulation is a critical factor, a mummy has less weight and pack size for the same insulation.

{ answered by Benedikt Bauer }