Sleeping Bag Length
Sleeping bags are sized by their length, and though this may seem obvious, the correct length for your bag should correlate with your height. For example, if you’re 6 feet tall, you should be sleeping in roughly the same length bag. However, don’t think that a 6-foot sleeping bag should fit like a latex glove. A 6-foot sleeping bag will actually measure roughly 6-foot 8-inches long, giving a 6-foot tall person the extra room needed for a correct fit. Why the extra room? When we lay flat, our spines decompress, our feet fall forward and our bodies spread out. As a result, sleeping bag designers compensate for this by adding a few extra inches to the length. The goal is to minimize excess space because excess space requires more energy to heat. So, choose a sleeping bag size with an appropriate length for you. Therm-a-Rest sleeping bags come in three sizes: small (5 ft. 6 in.), regular (6 ft.), and long (6 ft. 6 in.). Pick the sleeping bag size closest to your measured height.
Sleeping Bag Shape
The shape of your sleeping bag should reflect the style of camping you’re planning on doing. There are three basic shapes of bags: Mummy, Rectangular, and Semi-Rectangular. We’ll break it down to help you decide which shape best fits your style.
Mummy
The most popular shape, the mummy bag has a snug fit that tapers toward the feet, making it the warmest option. This shape allows the least amount of air between you and the insulating wall of the bag, meaning there is less air to heat. Due to its efficient shape, it’s also lightweight and packs easily, making it the ideal choice for backpacking or technical adventures that require packability but also a high degree of warmth. The downside? Room. A mummy bag can be restrictive compared to other shapes.
Rectangular
As the name implies, this is a non-tapered design, which is less efficient at heating, but also less restrictive while sleeping. Warm weather car campers often opt for rectangular-shaped sleeping bags due to the freedom of movement they provide. If comfort, not warmth-to-weight efficiency, is your main priority, consider this style of bag.
Semi-Rectangular
A hybrid between the mummy and rectangular shape, this is the go-between for fair-weather campers that require warmth but also desire the extra room for added comfort. While not as warm as mummy bags that can withstand 3 to 4 season camping, a semi-rectangular bag can work for fair-weather trips and also be efficient enough for shorter backpacking adventures.
Sleeping Bag Fit
Our sleeping bags' fits are carefully crafted to fit the needs of your adventure. Most of our Fast & Light bags fall under Performance Fit. This fit is tapered to maximize thermal efficiency and minimize pack size, while still providing some girth for comfort. Our Ultralight Fit is even further tapered and cuts down on internal space for those counting every single ounce.
For more comfort-minded backpackers we offer W.A.R.M. Fit. This fit is what you'll find in our Trek & Travel line of sleeping bags. We dove into our cold chamber to create the a balance of roominess and thermal efficiency. While slightly heavier and bulkier than Performance Fit, more internal space means you can sleep in whatever position you want.
Check out our blog post for more detailed information on this topic:
https://cascadedesigns.com/blogs/thermarest-gear/choosing-sleeping-bag-fit