In August 2022, REI Co-op product developer Lauren Bowman asked hundreds of gear testers of all shapes and sizes to hunker down in sleeping bag samples. Bowman wanted to take measurements while actual people used the bags to pinpoint optimal fit for real-world backpackers. So while testers played cards and read books in the bedding, she noted where the baffles pinched, gapped, sagged and bulged. The goal: to create better-fitting bags.
These fit sessions were part of a comprehensive REI Co-op initiative that looked critically and exhaustively at how well this piece of gear served the growing demographic that wants to spend time outdoors. Inclusivity motivated the reevaluation, explains Bowman.
Research and rigorous testing ensued, ultimately informing the design of nine new genderless sizes for three of the co-op’s most technical sleeping bags—the Magma 15, Magma 30 and Zephyr 25—in a big move away from limited sizing based on a binary gender model.
“If we say the outdoors is for all, how do we facilitate that by actually having bags that people can sleep in?” she asks.
The Sleeping Bags
Sleeping bag sizing hasn’t changed much since their 1876 invention by the redundantly named Welshman Sir Pryce Pryce-Jones (who also launched the first-ever mail-order catalog business). For decades, REI Co-op has mostly sold its house-brand sleeping bags in two sizes—regular and long—for men and women. While these bags worked for some people, shorter folks ended up with unnecessary space that cost them weight and warmth (the extra room compromises thermal efficiency). And because product girths didn’t vary, slender folks tolerated too-big bags while larger shoppers weren’t accommodated at all.
“We were hearing from some customers that they were frustrated trying to find the right fit,” explains Bridget Stephas, REI Co-op product designer. The desire to create better sizing led REI to widespread testing and fit sessions and, eventually, the debut of new sizes for three existing REI Co-op sleeping bags.
The Magma 15, Magma 30 and Zephyr 25 are now each offered in nine sizes instead of four, ranging from short narrow to long wide, and are no longer labeled by gender. Importantly, they maintain the same technical features backpackers expect from these long-standing sleeping bags, like a water-resistant finish, thoughtful pockets and a roomy footbox.
“We want to serve people that haven’t been well-served [by sleeping bags] in the past,” Meade said.
The Sizes
Determined to take a fresh look at a classic piece of backpacking gear, REI designers built on the brand’s 85 years of experience. “We wanted to make no assumptions,” explains Bowman, the product developer who played a driving role in the reevaluation.
REI commissioned a consulting company that specializes in apparel fit to conduct a large-scale study of Americans’ current bodies. Subjects included 150,000 people representing diverse shapes and sizes, ranging from 25 to 40 years old. “We got this massive wealth of body-scan data,” explains Bowman. The results revealed two discoveries.
One was that the current line of REI Co-op premium, backpacking-oriented sleeping bags only provided an optimal fit for just over half of the people scanned in the study. Some couldn’t use them at all because they were too narrow.
“To get maximum thermal efficiency out of a backpacking bag, you want a close-to-body fit that allows some air circulation but not too much,” explains Jon Almquist, REI Co-op product manager. “That way, you exploit the full benefit of the high-quality down we put in the bag.”
Related Reading: How to Choose Sleeping Bags for Backpacking
The study data also indicated that fit trends didn’t vary much between male and female bodies. “Overall, men’s shoulders trend a little wider, but the difference is so small in relation to how loose over the body a sleeping bag fits that it becomes negligible,” Bowman says. Sleeping bags aren’t like jeans: Even the optimal, body-hugging cut preferred by performance-minded backpackers is forgiving enough to skim over slight variations in body shape.
With the body-scan data suggesting that gendered fits aren’t necessary, the product creation team considered temperature ratings, which typically vary for men and women. According to test protocols used by the International Organization for Standards (ISO), heated mannequins are placed inside a sleeping bag to evaluate heat loss. The calculated results produce various temperature ratings: The bag’s T-Limit rating indicates the temperature down to which a warm sleeper (assumed to be male) will feel comfortable; the T-Comfort rating denotes the comfort range for cold sleepers (assumed to be female). Women’s bags generally use the T-Comfort rating, while men’s bags display the T-Limit number.
According to test protocols used by the International Organization for Standards (ISO), there are two different temperature ratings: one for cold sleepers (T-Comfort) and one for warm sleepers (T-Limit). Women’s bags often use the T-Comfort rating, while men’s bags display the T-Limit number.
Yet fit also influences insulation, notes Bowman. “A body-hugging fit is warmest, while a semifitted bag allows more room for various sleep positions but loses some thermal efficiency,” she explains. For instance, the relaxed shape of a rectangular car-camping bag loses the most heat but emphasizes comfortable movement.
The product creation team therefore decided to focus on fit, regardless of gender. Starting in spring 2024, the Magma 15 and Magma 30 (the co-op’s performance-oriented backpacking bags stuffed with 850-fill, water-resistant down) come in nine sizes each, from short narrow to long wide. The synthetic-fill Zephyr 25 also comes in nine sizes. Honed by meticulous fit sessions, the new sizing options provide an optimal fit for nearly all of the bodies scanned in the comprehensive study.
The bags still undergo ISO temperature testing, only now their rating represents the midpoint between the T-Limit and T-Comfort figures (which are also printed on the bags for consumers who want to see the full range). Thus, the new bags are slightly warmer than previous men’s and unisex models.
“We didn’t just make a men’s bag in nine sizes,” says Bowman. “Really, they’re for everyone, of all body types and different sizes.” Women’s data was just as influential in the bags’ creation as men’s input—a key difference from previous products made 40 years ago, explains Bowman. “We landed on non-gendered bags through research.”
The Results
The unified temperature ratings simplify the shopping process for men and women. They also allow backpackers to choose the bag that suits their body shape and temperature needs regardless of gender: Men who sleep cold, for example, no longer need to browse the women’s offerings to get the optimal product. And nonbinary backpackers no longer have to start the shopping process by choosing among binary gender labels.
As for the biggest benefit to the new genderless size range? More backpackers can find their best sleeping-bag fit and enjoy a good night’s sleep outside.