For the three nights in early winter, as temperatures slipped into the teens and single digits Fahrenheit outside my tent on the snow in Idaho’s Boise Mountains, I zipped up snugly inside my sleeping bag and lay on this fat, well-insulated air mattress, briefly considering that I might feel cold before morning. And every morning, I awoke after sleeping longer and later than I normally do in my bed at home, feeling incredibly well rested and realizing my bag and air mat could have handled even colder temps.
While the bag I used certainly gets some credit for my comfort on those frigid nights (read my review of that sleeping bag), it’s a well-known fact that, ounce-for-ounce, the air mattress underneath you delivers more insulative value than your bag—especially on snow or frozen ground, which can quickly drain your body heat.
The outdoor industry has, since January 2020, employed a new standard test, ASTM F3340-18, to measure R-value—or how well an air mat or any kind of sleeping pad insulates against cold ground to prevent convective heat loss from your body. Only air mats with a minimum R-value of 4.5 to 5 are adequate for sleeping outside on frozen ground with below-freezing air temperatures.
The Sea to Summit Ether Light XT Extreme Insulated Air Mattress performs well in those conditions thanks to Thermolite hollow-core insulation, which lofts inside the mat, giving its four unisex versions an R-value of 6.2, warm enough for sleeping on frozen ground in temps well below freezing. The women’s-specific Ether Light XT Extreme versions have additional Thermolite insulation, giving them a 6.3 R-value. Few air mats have an R-value that high—although two Therm-a-Rest models have a 6.9 R-value, the NeoAir X-Therm (read my review) and the NeoAir X-Therm MAX. Both also cost about $30 more but are significantly lighter and more compact than the Ether Light XT Extreme—though not, I think, as comfortable.
A fat four inches/10cm thick, the Ether Light series of air mats incorporates the brand’s Air Sprung Cells, made with a matrix of interconnected air chambers that individually conform to your body. Mimicking a pocket-spring mattress in the way they distribute your body weight and prevent hipbones or shoulders from bottoming out on the hard ground, those cells create a sleeping experience that feels more like a bed than lying atop a big, flat balloon.
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The Air Sprung Cells also use internal TPU fabric loops to bind the top and bottom layers of shell fabric, enabling more spacing between cells and more air pockets, all of which translates to more cushioning and less weight.
At 21.7 inches/55cm wide at the shoulders and tapering to 16.5 inches/42cm at the foot, the regular Ether Light XT Extreme provides a bit more width than standard regular-size air mats—I never felt like I was on the edge, about to roll off. The six-foot/184cm length is standard for regular-size backcountry air mats. The women’s-specific Ether Light XT Extreme versions are less than an inch wider, six inches shorter, and a bit lighter in the two sizes.
The Ether Light’s two-piece valve has separate ports for inflating and deflating, and deflating takes just a few seconds and makes for a much easier and faster method of packing up the air mat.
The 30-denier and 40-denier face fabric is more durable than some air mats and features extruded lamination and an anti-microbial treatment to inhibit fungal growth inside the mat, both features helping to extend the mat’s life.
The latter is most likely to come from inflating the mat with your breath, but that can be avoided by using Sea to Summit’s Airstream Pump stuff sack (2.2 oz.), which comes with the Ether Light air mats. It allows you to efficiently inflate the mat by blowing a light breath into the open sack and rolling the air into the mat—a much easier experience than making yourself dizzy blowing air directly through the valve. S2S says you use 80 percent fewer breaths, a time and energy saver that also reduces moisture entering the mat—even more important in sub-freezing temperatures, when it will dry out less easily.
Still, I found it requires repeatedly filling and rolling the bag, which becomes a bit tedious. I have substituted the larger and much faster Exped Schnozzel PumpBag UL bag ($39, 2 oz.), which doubles as an ultralight stuff sack for clothing, too.
The Pillow Lock is a nice feature that consists of non-stick patches applied after purchase (peeling and sticking them into place where indicated on the mat) that hold a pillow in place while you’re sleeping.
For its dimensions and R-value, the Ether Light XT Extreme is relatively light and compact at barely more than 1.5 pounds (regular size) and measuring 6.9×9.4 inches/17.5x24cm packed, slightly larger than a football.
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Exceptionally comfortable and highly insulated while remaining reasonably lightweight and packable for a winter air mattress, the Sea to Summit Ether Light XT Extreme Insulated Air Mattress will appeal to many backpackers, climbers, backcountry skiers and other adventurers who sleep on snow or frozen ground.
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You can support my work on this blog, at no cost to you, by clicking any of these affiliate links to purchase a unisex Sea to Summit Ether Light XT Extreme Insulated Air Mattress at backcountry.com, moosejaw.com, or seatosummit.com, or a women’s Ether Light XT Extreme Insulated Air Mattress at seatosummit.com.
Whether you’re a beginner or seasoned backpacker, you’ll learn new tricks for making all of your trips go better in my “12 Expert Tips for Planning a Backpacking Trip,” “A Practical Guide to Lightweight and Ultralight Backpacking,” and “How to Know How Hard a Hike Will Be.” With a paid subscription to The Big Outside, you can read all of those three stories for free; if you don’t have a subscription, you can download the e-guide versions of “12 Expert Tips for Planning a Backpacking Trip,” the lightweight and ultralight backpacking guide, and “How to Know How Hard a Hike Will Be.”
NOTE: I tested gear for Backpacker magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See The Big Outside’s Gear Reviews page for categorized menus of all my reviews and expert buying tips.