Sea-to-Summit Etherlight XT Extreme Sleeping Pad Review

Sea-to-Summit Ether Light XT Extreme Sleeping Pad Review

The Sea-to-Summit Ether Light XT Extreme Sleeping Pad is an insulated inflatable sleeping pad that is 4″ thick and has an R-value of 6.2 making it suitable for cold weather backpacking and camping use. Weighing 25.6 oz, it’s the winter version of the three-season Sea-to-Summit Ether Light XT Sleeping Pad which I use for tent and tarp camping and swear by because I sleep so well on it.

Sleeping pad comfort is even more important in winter because there’s so little daylight and you spend much more time in your tent and sleeping bag.  If a good night’s rest is a priority for you, I’d encourage you to try the Ether Light XT Extreme Sleeping Pad from Sea-to-Summit. Although, with a pad this comfortable, you might never want to get out of your sleeping bag to go winter backpacking and snowshoeing!

Specs at a Glance

  • Weight: 25.6 oz /720g (pad only)
  • R-value: 6.2 (ASTM F 3340-18 Pad R-Value Standard)
  • Type: Inflatable
  • Valve-type: Flat
  • Gender: Men’s, a Women’s Model is also available
  • Dimensions: 72″ x 21.5″ (25″ widths and 78″ long lengths, also available)
  • Thickness: 4 inches /10cm
  • Insulation: Synthetic insulation
  • Packed dimension: 6.9″ x  9.4″
  • Antimicrobial treatment: Yes
  • Included insulation sack: Yes (adds 2 oz to pad weight)
  • Materials: 30d / 40d nylon

Pad Comfort and Quiet

The sleeping surface of the Ether Light XT Extreme is made up of air-sprung cells, which mimic a pocket spring mattress so that the surface of the pad conforms to your body shape regardless of whether you sleep on your back, side, or stomach. The pad’s 4-inch thickness also helps ensure that your knees and elbows won’t bottom out at night when you roll around and helps mask any rocks and roots that may lie under your tent floor.

The Ether Light XT Extreme is available in multiple widths, lengths, and with a mummy or rectangular shape.
The Ether Light XT Extreme is available in multiple widths, lengths, and with a mummy or rectangular shape.

The Extreme is insulated with a reflective platinum coating and 2 layers of Thermolite synthetic insulation positioned inside the top and bottom sides of the pad. This helps reduce convective heat loss keeping the surface of the pad warmer, quieter, and more comfortable to the touch. The pad’s 30/40d nylon covering offers a warm hand as well as added puncture and abrasion resistance.

Flat Valve and Pump Sack

The Ether Light XT Extreme comes with its own combination stuff sack/pump sack for ease of inflation. It mates to the pad’s flat valve, which is a three-way valve: one for inflating the pad, with an integrated nipple that lets you release air for more comfort, and a closed cap for closing the valve completely. If you lift both caps to deflate the pad, the air quickly rushes out of the big valve hole, so you don’t have to spend time evacuating the air or rolling up the pad multiple times to force it all out. Flat valves are also much more durable than stick valves since they don’t require a screw-type lock and roll-up flat.

The Extreme’s stuff sack/pump sack weighs 2 oz more. You can leave it behind and inflate the pad by mouth if you want to save on gear weight. The pad has been treated inside with an anti-microbial agent to ward off the growth of fungus should you choose to inflate the pad by blowing it up manually.

Sea to Summit Pads include a pillow attachment system that really does keep your Sea-to-Summit pillow on the pad at night.
Sea to Summit Pads (both left and right) include a pillow attachment system that really does keep your Sea-to-Summit pillow on the pad at night.

Pillow Attachment

The Ether Light XT Extreme comes with 4 velcro strips that you can stick onto the top of the pad. These hold a Sea-to-Summit pillow in place so it doesn’t move off the pad at night. It works great. I use a 2.5 oz Sea-to-Summit Aeros Down Pillow, but the pillow-lock system works with any of the Sea-to-Summit’s inflatable pillows.

R-Value for Winter Camping

The Ether Light XT Extreme has an R-value of 6.2, measured using the ASTM F 3340-18 standard that was introduced in 2020. This is the same R-value measurement test protocol used to rate NEMO, Exped, Big Agnes, and Therm-a-Rest Sleeping pads, among others, making it possible to compare their ability to insulate you from the ground. Many inexpensive brands, including Klymit, don’t test their pads using this standard (and some just make up their R-value ratings) so buyer-beware.

Air Temperature (F):50433629221580-7-14-21-30
Minimum R-Value11.522.533.544.555.566.5
Air Temperature (C):1062-2-6-9-13-18-22-26-30-34
Minimum R-Value11.522.533.544.555.566.5

When choosing a sleeping pad for winter backpacking and camping, we recommend using a pad or combination of pads that have a minimum R-value of 5 or more for subzero temperatures. R-values are additive, so you can combine two pads to increase your warmth level. Women need higher R-values pads because they have lower body mass than men and generate less heat. An additional R-value of 1 is usually a good hedge for women and other cold sleepers.

But It’s Heavy

Gear weight is always a consideration when winter backpacking because you have to carry so much more water, food, stove fuel, insulation, and traction devices like snowshoes, crampons, or microspikes. In addition to a sleeping pad, you always want to carry a foam sit pad or a foam sleeping pad when winter camping so you have something warm to sit on when melting snow or cooking. These activities can take as much as 2 hours each day or more if they turn into social occasions.

Bring a foam pad to sit on when you melt snow and cook.
Bring a foam pad to sit on when you melt snow and cook.

You can use a lighter-weight sleeping pad and combine it with a foam sleeping pad to get to an R-value of 5 or 6. I did this for many years myself, carrying an earlier model NeoAir XTherm Pad (before 2020, when it had an R-value of 5) and a folding foam Therm-a-Rest Zlite (R-Value of 2) which I sat on when melting snow and placed under my sleep pad at night.

You have to decide whether you want to carry one pad like the Extreme and a small foam sit pad or two sleeping pads, including an inflatable pad and bulky foam pad, which can be awkward to carry in winter. Personally, I finally got rid of all my NeoAir XTherms this year because I sleep so much better on Sea-to-Summit’s Ether Light XT pads. Weight is far less important to me than a good night’s sleep. As long as I carry a small foam sit pad, like the NEMO Chipper for sitting on snow, I can carry the Ether Light XT Extreme and have a more packable sleep insulation system.

But you have to decide on your priorities:

  • Do you want the lightest possible winter sleeping pad system or the most comfortable?
  • Do you want the extra “insurance” that carrying a full-length foam pad provides if your inflatable pad leaks or shits the bed?
  • Do you want to minimize the amount of bulky gear, like a foam pad, that you have to strap to the outside of your backpack?
  • Can you form a splint with an inflatable pad, like you can with a foam pad?
  • And so on.

Winter (High R-Value) Sleeping Pad Comparison

Sleeping PadTypeThicknessWeightASTM 3340 R-Value
Sea-to-Summit Ether Light XT ExtremeAir Pad4.0"25.6 ozR=6.2
NEMO Tensor Alpine UL InsulatedAir Pad3.0"17 ozR=4.8
Therm-a-Rest NeoAir XliteAir Pad2.5"12 ozR=4.2
Therm-a-Rest NeoAir Xlite Women'sAir Pad2.5"12 ozR=5.4
Therm-a-Rest NeoAir XThermAir Pad2.5"15 ozR=6.9
Exped SynMat UL WinterAir Pad3.5"21 ozR=5.2
REI Flash ThermalAir Pad2"19 ozR=4.9
Mountain Equip Aerostat DownAir Pad2.8"20.4 ozR=5

Recommendation

The Sea-to-Summit Ether Light XT Extreme Air mattress is a super comfortable sleeping pad with air-sprung cells that mimic a spring mattress. A full 4 inches thick, it conforms to your body shape, regardless of whether you’re a back, side, or stomach sleeper. A flat valve and durable exterior fabric increase durability and reliability, while an R-value of 6.2 helps ensure that the rest of your winter sleep system will perform optimally at the temperature that it is rated for. If you don’t like the winter sleeping pad you currently own and quality of sleep is a priority, I can recommend the Ether Light XT Extreme. It really is a warm, durable, and comfortable winter sleeping pad.

Disclosure: Sea-to-Summit provided the author with a pad and pillow for this review.

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10 comments

  1. Have You had any durability issues with those pads? I’ve read some reviews claiming that delamination at the welds leading to micro leaks is quite common. I can’t decide whether to buy Woman’s STS insulated or xlite wide.

    • No – no issues. But they also have a no-questions-asked return policy if it helps. Frankly – you couldn’t pay me to sleep on an Xlite ever again. They were revolutionary when they came out but they’re just not that comfortable compared to the S2S pads.

      • Thanks for the info – indeed STS looks like it’s going to handle weight distribution and side sleeping much better than xlite

  2. I now have 3 of the Sea to Summit Ether Light XT pads, I won’t use anything else, and like Philip, I have sold off many of my other pads. Mostly I wanted to share a real world weight comparison, all 3 pads are the large tapered shaped men’s versions.

    XT Uninsulated. 16.5oz (Pad only). 18.1oz (Inflation / Stuff sack and patch kit included)
    XT Insulated. 21.0ox (Pad only). 23.2oz (Inflation / Stuff sack and patch kit included)
    XT Extreme. 33.4oz (Pad only). 35.8ox (Inflation / Stuff sack and patch kit included)

    I’ve used the uninsulated down to 40 degrees, and the insulated down to 20. In both cases I felt like I was pushing the temperature limits an bleeding some heat through the pad, I’ve yet to test the Extreme in cold weather, but my hope is that it will feel toasty down to 0 Fahrenheit, and adequate if it dips colder.

  3. After your earlier review of the STS Etherlite XT I purchased one and was not dissapointed. It is without question the most comfortable sleeping pad I’ve ever owned, and light enough too. The only feature I did not like was the combo stuff sack and inflation sack, which is really two sacks stitched together and I find awkward to use. I remedied that on my sewing machine and now have two separate sacks, one to stuff and one to inflate. It truly is much faster.

    Is there such a thing as too warm? Would it make any sense to sell my XT and get an extreme for use in all conditions?

    • Hi Ben. I use an Exped pack liner/pump bag called a Schnozzel to inflate the pad because I get multiple uses out of it.
      I think you can use a high r-value pad for all seasons, but I’ve had knock-down drag-out fights with some of my readers who argue the opposite and claim to be too warm. Personally, I’d keep the regular XT for 3 season use just because it’s so much lighter.

  4. I used one of these four nights last week. It’s the most comfortable pad I’ve ever used. I slept better than I have in years camping. Toasty warm and no achy back when I woke up. That was money well spent and weight worth the effort.

    • I have to amend my enthusiasm a bit. The previous trip noted above, lows were in the 40s. Last night, with lows in the upper 20s, I was uncomfortably cold from below using this pad. I’m going to contact S2S to ask if they’ve had any problems like this.

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