The primary difference between a mummy and a rectangular sleeping bag is the shape but it’s the function that distinguishes the two. A mummy bag tends to be much warmer because of the fact that it fits so much closer to the body and you can cinch it down. You can zip yourself up and it closes down and your only face is sticking out. Some people may find it a little uncomfortable because they’re too narrow but for a colder climate, this is ideal because you want that heat retention. Mummy bags also tend to pack small so if you’re a backpacker, this a great option for you.
Rectangular or square sleeping bags, on the other hand, provide plenty of room for your legs and arms to starch out. Some people find it more comfortable because of its shape or you can even unzip it and use it as a comforter. The downside is, they are heavier than mummy bags and do not pack down small. So if you’re a backpacker, this option may not be ideal for you. You may have also heard the term semi-rectangular sleeping bags also known as “modified mummy” or “barrel” shape. It includes a variety of shapes. They offer a range of options that compromise between warmth and roominess.
Which one is right for you?
When choosing a sleeping bag, it’s important to keep in mind that the shape of the bag is crucial for the type of activity you’ll be doing. For example, if you’re planning a backpacking trip, consider a lightweight mummy-style bag because while backpacking, you’ll be carrying weight mostly on your shoulders. On the contrary, for car camping or family camping when weight is not crucial, you could choose a heftier rectangular bag that can provide more room for you to sprawl or you can completely unzip it and use it as a blanket.
The following are a few things to consider when deciding between the sleeping bag’s shapes:
Even for backpacking, you can choose the coziest, roomiest, and warmest sleeping bag out there but at the end of the day, you’ll be carrying some extra weight on your back. So you need to strike a good balance between weight and warmth. A typical sleeping bag weighs between 1 to 3 pounds depending on the manufacturer, features, and type of insulation. Also, budget sleeping bags like REI Co-op Trailbreak, do not pack down small.
Mummy bags are a little narrower at the feet and wider at the shoulders than rectangular bags. They are the most efficient bags when it comes to heat retention. So if you’re backpacking and weight is a major concern, a mummy bag is the right choice for you. In contrast, rectangular bags give you a lot more space for comfort but they tend to be heavier. This feature makes them a good option for car camping and family camping.
As I already mentioned, the warmth of a sleeping bag is associated with its shape. The mummy bags fit your body well; like at your feet and shoulders and retain heat well. Rectangular bags fold over your body and they’re great for car camping but they may be too heavy for backpacking.
Premium down sleeping bags pack down super small and it’s a big selling point for manufactures. You can also pick a compression sack to take advantage of the small stuffed size potential of the bag. On the other hand, synthetic bags don’t pack small and they’re not even close to down. So if pack size is one of your concerns, consider a down bag.
Mummy Vs. Rectangular Bags: Comparison Table
|Weight||Usually lightweight but that depends on the type of insulation||Usually heavy|
|Roominess||Not very roomy||Very roomy|
|Warmth||They’re the most heat efficient||You lose some warm air at shoulder and large foot-box is not ideal for heat retention|
|Packed size||Packs down super small if you get a premium down bag||Large pack size|
|Versatility||Not much versatile||Some bags can be completely unzipped and you can use them like a blanket|
|Hood||Yes, comes with hood||No hood option|
|Price||The high-end models tend to be more expensive||You can get a decent bag at an affordable price|
|Best use||Backpacking and UL backpacking||Car and family camping|
Mummy bags are the most commonly thought of sleeping bag’s shape when it comes to what to get and they are the kind of tried and true options while a squarer cut bag provides more room for your feet to kick around. However, the mummy shape has a pretty narrow foot-box and they’re classic for a reason that they’re very efficient in keeping people warm and you don’t waste a lot of extra space inside therefore having to have your body spend more energy keeping that space warm.