Sea to Summit Ether Light XT Extreme Insulated Air Sleeping Mat Gear Review

Winter camping. Who’s afraid of it? And for what reason? I’ve met many folx who adore three-season backpacking and simply cannot wait for temperatures to warm up so that they can get back to their favorite activities. I always ask, “Why wait til spring?!” Winter camping is extremely fun, and you can indeed be incredibly comfortable. You just need the right gear.

In my opinion, one of the most essential elements of a good winter camping setup is the sleeping pad. Of course, having a warm enough sleeping bag is also important (and warm clothes and the right shoes and and and…). But when it comes to a comfortable and safe night’s rest, insulation between you and a very cold ground is critical. I recently tested the Sea to Summit Ether Light XT Extreme sleeping pad and feel as confident as ever that winter camping can be for everyone who wants to do it.

close-up of black Sea to Summit ether light extreme sleeping pad on snow

Ether Light XT Extreme Insulated Air Sleeping Mat At-A-Glance

  • MSRP: $219 – $249
  • Weight: 25.4 oz – 37 oz. (depending on chosen design)
  • Thickness: 4 in / 10 cm
  • Fabric: Durable 30 denier/ 40 denier nylon
  • R-Value: 6.2
  • Season Rating: 4 Season

Intended Use

The Sea to Summit Ether Light XT Extreme Insulated Air Sleeping Mat is intended for cold-weather backpacking and camping.

Circumstance of Review

I tested the Ether Light XT Extreme on winter backpacking and camping trips in western North Carolina and Utah. Conditions ranged from extremely humid to extremely dry, with generally cold temperatures, mostly clear skies, and sometimes a fair amount of snow. For the most part, I was using my Feathered Friends Tanager 20 CFL Sleeping Bag (which I still adore, by the way) and a mixture of double- and single-wall tents.

Sea to Summit Ether Light XT Extreme Features

ASTM-tested R-Value: The key to a good winter sleeping mat is an appropriate R-value. As I’ve described previously, the R-value is the amount of thermal resistance (“R”) per unit of a barrier’s exposed area (in this context, the barrier we’re talking about is the sleeping pad). Higher R-values indicate greater thermal resistance, which experientially translates as losing less heat into the ground.

R-values of 4 and above are rated as appropriate for all seasons, and R-values of 6 and above are best for extremely cold conditions. The Ether Light XT Extreme’s R-value rings in at a toasty 6.2. This has been lab-tested per the ASTM industry standard. The Ether Light XT Extreme’s high R-value is, in part, made possible by two of the mat’s innovative technical features: the cells that that support the body’s weight (Air Sprung Cells) and the insulation inside those cells (Thermolite HL-1).

Air Sprung Cells: To summarize from Sea to Summit, these cells form a network of interconnected air pockets that are ultimately what support your weight. To make the overall cell thicker with better structural integrity, the top and bottom pockets are also connected.

Thermolite HL-1: Again summarizing from Sea-t0-Summit, HL-1 is a fiberfill, high-loft insulation that lofts up in the Air Sprung Cells. This prevents heat loss through convection—i.e., transfer of heat from one place (your body) to another place (the air, the ground).

Airstream Pumpsack: This mattress pump is specifically designed for “big volume” mattresses. The pump sack is conveniently integrated into the stuff sack, so it’s not an additional loose sack you have to keep track of. To inflate the Ether Light XT Extreme, you attach the pumpsack to the mat and blow a breath into the pumpsack, then capture the air in the pump sack and roll it into the mat (see this video at 1:22). There are several benefits of this inflation system: 1) it is exponentially faster, 2) it is exponentially easier, and 3) it reduces the amount of condensation entering the mat, thereby reducing gradual deflation.

orange stacked valve of sea to summit ether light xt extreme sleeping pad with cap open

Ether Light XT Extreme Pros

Warmth: As someone who is perpetually cold, I say with confidence that this gem will keep you insulated from the ground. That said, the overall experience of warmth boils down to much more than the mat itself. It’s essential to pair the Ether Light XT Extreme with an appropriately rated sleeping bag and a shelter that will adequately protect you from the elements.

Easy inflation: The time-consuming, lightheadedness-inducing drudgery of inflating your sleeping mat is forever changed by this stroke of genius. It fills me with an unreasonable amount of joy every time I use the Airstream Pumpsack.

Comfort: It is very cushy.

The noise factor: “Does it crinkle every time you move?” In my experience: no, it does not. That said, I generally sleep like a dead person and am largely unaffected by things like this, so I admittedly may not be the best judge.

Care for People and Planet: Sea to Summit is publicly vocal about and engaged with matters relating to climate change and environmental sustainability, as well as fair labor practices and community partnerships. Read more about what they’re up to here.

Ether Light XT Extreme Cons

“4 Season”: Even though the Ether Light XT Extreme is technically usable in all seasons, it’s best for cold-weather camping. And in my opinion, that actually makes it a single-season mat. For someone who has just gotten into backpacking and doesn’t have a ton of financial resources, this would be a drawback of the warmth of this mat.

You’d likely be way too warm using the Ether Light XT Extreme in the summer (in most climates). In any case, I assume most people would prefer to use a lighter and smaller pad whenever possible. So, this may not be a realistic piece of gear for someone who’s just dipping their toes into winter camping.

If that’s you, know that R-values are additive. That means if you have a couple more versatile 3-season pads with R-values around 2–3, you can stack them on top of each other to create a higher R-value. This might be a nice first step to try out winter camping before investing in an expensive cold weather mat like the Ether Light XT Extreme.

Size and weight: In my experience, when you have a piece of gear that’s truly warm, there is usually a penalty of size and/or weight. (Of course, there are exceptions. This is a big reason why I love the aforementioned Feathered Friends Tanager: incredible warmth-to-weight ratio and very compact.)

In this case, the cost for the Ether Light XT Extreme’s high R-value is both size and weight. This is a very big/thick sleeping mat, and the regular size (suitable for someone up to six feet tall) weighs 25.4 ounces. I’ll spare you the math; that’s over 1.5 pounds. That’s more than my single-wall tent weighs! The packed size of the regular mat is also quite cumbersome and may require some highly strategic packing (or a larger pack for winter trips). I wish there were a “short” or “petite” size option for those of us closer to 5 feet.

To be fair, to some extent, the size and weight are an inherent trade-off for the amount and quality of materials needed to adequately prevent heat loss to a frozen ground. Because of this, it feels slightly unfair to call this a “con.” On the other hand… it really feels like a con when you’re packing for a trip and realize how hefty your pack is. (And some pads achieve higher R-values for less weight, like the Therm-a-Rest NeoAir XTherm).


close-up of black sleeping pad with "Etherlight XT Extreme" printed in white and orange lettering

If you’re not sure if winter camping is for you, you might not want to spring for this mat until you’ve gotten some practice. But if you’re ready to go for it or you’re a seasoned winter backpacker looking for your next gear investment, the Sea to Summit Ether Light XT Extreme is a very warm, comfortable option for cold-weather camping and backpacking.

Shop the Sea to Summit Ether Light XT Extreme Sleeping Pad

Comparable Sleeping Mats

Therm-a-Rest NeoAir Xtherm NXT Sleeping Pad 
MSRP: $230
R-Value: 7.3

REI Co-op Helix Insulated Air Sleeping Pad
MSRP: $159
R-Value: 4.9

The Sea to Summit Ether Light XT Extreme sleeping pad was donated for purpose of review.

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