Sleeping bags basically come in 3 different shapes, but why should you care? You just want something that’s warm and comfortable to sleep in, right? Perhaps weight is also an issue, but the shape of the sleeping bag? Yes, the sleeping bag shape is important. Besides the material used, the shape or design of a sleeping bag is the most important factor in determining how warm it is, how heavy it is and perhaps also how comfortable it is!
Mummy sleeping bags are more narrow in the foot-end than in the head-end. They sort of resemble the way a mummy is wrapped up, if you’ve ever seen one. Since your feet don’t require as much space as your shoulders, it’s a pretty logical way to construct a sleeping bag. The tighter fit of the mummy bags means that there will be less air inside the sleeping bag and less surface area between the warm interior and the cold exterior surrounding you. The simple effect of this is that the mummy sleeping bags are generally warmer. Or rather, they have better insulation and don’t give away as much of your nice body heat to the cold environment.
Mummy bags are also generally more lightweight, since the design uses slightly less material to wrap around you than a barrel one does. For these reasons, the mummy sleeping bags are generally preferred for lightweight backpacking, hiking and trekking.
Now on to the barrel shaped sleeping bags. With all the excellent qualities of the mummy bag, why would you want to consider a barrel or rectangular shaped bag?
Some people feel too crammed up in the tight fit of a mummy bag. Claustrophobic. If you are the type who like to wiggle your feet and toss and turn in your sleep, the barrel sleeping bag will allow you more freedom of movement during the night.
If you are camping out in the open in cold conditions, there is also the advantage of being able to stuff some of your gear into the sleeping bag with you. Definitely socks. And gloves. Some trekkers and hikers even like to keep their shoes or boots warm for the morning, by sleeping with them in the bag! The more roomy barrel shaped bags allow you to do just this. Just remember to keep your muddy boots in a plastic bag so they don’t make your sleeping bag dirty. You can even use the little stuff sack that usually comes with the sleeping bag.
The rectangular sleeping bag is the least warm of the 3 designs described here. Most of these sleeping bags have a quite large opening. It’s nice for allowing you – and your hands – to move in and out of the bag as much as you like. But at the same time it also allows some of your body heat to escape. For summer use, that might not be a big problem though. Rectangular sleeping bags also tend to be some of the cheapest sleeping bags around. A bit more bulky as well. But for a lot of casual use, rectangular sleeping bags are the ‘best deal’. After all, you don’t need a high-altitude mountaineering bag for a weekend summer camp at the local lake.