Mountain Equipment Snowline SL Sleeping Bag

© Toby Archer
Toby Archer checks out a top of the range bag that allies super light technology (hence the "SL" tag) to enough top quality goose down to protect the user from punishingly cold temperatures.

There's no getting away from it, -20 is cold. Your body, if not working hard to make heat, does not have long at that temperature before the pervasiveness of the cold seeps in, first cooling your extremities and then your core with, of course, the predictably disastrous results. The idea then, of sleeping out at such temperatures, is faintly ridiculous. The peoples of the north and of the steppes evolved with mobile shelters; the igloos of innuit, the lavvus of Sami, yurts in Central Asia; places where the crushing cold could be banished enough to make sleeping possible. Mountaineers and other self-propelled travellers in cold climates often don't have that choice; any shelter light enough to carry, be it tent, tarp of bivvy bag, can protect against wind and snow, but not against deep cold. To sleep we have to rely on our sleeping bags.

The Snowline SL, "a good night guaranteed" to -20.  © Toby Archer
The Snowline SL, "a good night guaranteed" to -20.
© Toby Archer

Perhaps making a very warm sleeping bag wouldn't be too complex if weight was not an issue; but, to slightly change Keith Bontrager's aphorism from bike design, we have: “warm, light, cheap. Pick two.” Using a synthetic bag over slimmer down bag can produce a very warm sleeping system, but light it is not. If you are pulling a pulk, this is the economical way to go, but no one wants to try and carry two sleeping bags in their pack and climb (or even just ski or backpack). A top of the range bag like the Mountain Equipment Snowline SL may well be amongst the most expensive pieces of mountaineering equipment kit anyone is likely to buy, but it is a marvellous piece of engineering and design where everything has been done to make it as warm as possible for its relatively small weight (1315 grams). It's just an inescapable fact that a sleeping bag warm enough to protect you from very low temperatures, whilst still being light enough to carry, is going to cost a lot.

The Snowline SL's excellent hood is central to its warmth.  © Toby Archer
The Snowline SL's excellent hood is central to its warmth.
© Toby Archer

So how do you make a bag that keeps you warm at -20? Take 800 grams of top quality, 850+ of down and stick it between a couple of layers of nylon? Not really. Of course high quality down is central but a look at Mountain Equipment's workbook and website shows the huge complexity of stitching inside the bag to create shaped baffles that keeps the down in place and lofted to make the most of its remarkable insulating properties. The foot end is shaped and made of 4 separate down chambers; the hood made up of eight. Double baffles stop the zip from leaking heat, and even side seams are offset and lowered to avoid potential cold spots. The outer fabric is new lightweight version of ME's now well known Drilite, breathable and highly water resistant. Considered in three dimensions, you can start to appreciate just how hugely complicated the sewing must be to make such bags, even before you factor in the costs of the top of the range materials and down.

A wee nip of Talisker for inner warmth as the temperature drops towards -20.  © Toby Archer
A wee nip of Talisker for inner warmth as the temperature drops towards -20.
© Toby Archer

But does all this design work on the Snowline SL work in the (snow)field? From my testing I can say, categorically, yes. I actually think that the Snowline SL works better than ME say it will. Using the the EN 13537 standard for bag testing, the Snowline is given a comfort rating of -9; a comfort limit rating of -17; and an extreme limit of -37. We can safely ignore the extreme limit, that's basically a theoretical limit where you won't actually die. I've found the comfort limit with EN 13537 to be very accurate for me with two previous sleeping bag reviews, but after my first night at -17 in the Snowline I was left with the impression the bag would go lower easily. ME believe that for technical reasons EN 13537 doesn't work well for bags designed for around -20 or lower (something that Marmot agrees with) and their main Extreme expedition range isn't EN tested as a result. To help address this they have introduced their own “good night's sleep guarantee” rating in addition to EN 13537.

The sun rises over the frozen sea. -20 in the Turku archipelago, SW Finland.  © Toby Archer
The sun rises over the frozen sea. -20 in the Turku archipelago, SW Finland.
© Toby Archer

For the Snowline SL they claim -20. Making such statements is fraught with problems; ME's guarantee is based on the bag being “comfortable for an experienced user” and that's rather open to interpretation. For instance, I doubt many women, experienced or not, would be comfy at that temperature just due to physiological differences. Nevertheless, I slept out for a number of nights where the temperature was at or lower than -20 and slept well. The coldest night I used the Snowline for got down to -22.7 by dawn, the chest area of the bag was covered in thick frost crystals from my breath by morning but I slept soundly for 7 hours. Most of the coldest nights were done just sleeping under the stars without tent, tarp or bivvy bag, but otherwise I do stack the odds in my favour - this is what being an “experienced user” presumably means.

For winter camping I use a Z-rest and three quarter length ultralite Thermarest (rucksack under my feet to give double protection there too) and make sure I've eaten something before bed. At -17 I was sleeping just in a base layer, socks and a hat, for -20 I added a micro fleece top, and for -23, micro fleece trousers too. In each case I slept fine; if you move during the night and push against the side, or perhaps break the seal of the baffles over the zip, you quickly sense a cold patch and that will wake me, but once I move back into a stable position in the bag, the cold spot goes and I go straight back to sleep. Overall, the Snowline SL is the warmest sleeping bag I've ever had the pleasure of trying.

There is more to a good sleeping bag though than simple warmth, it needs to be 'usable' too. The Snowline SL is ME's “mountain fit”, rather than the slimmer and lighter “alpine fit”. I think it is quite a roomy bag, I've kept my SLR in it's case and a gas cylinder down by the feet without feeling cramped. There is enough room to be able, with the bag fully zipped up, to reach down and pull on my down-filled 'sleeping socks', something not possible with bags with slimmer lower sections. I think the room is a wise choice for a bag designed for climbers: wearing layers of clothing in bed; filling your bag up with 'stuff' that needs to stay warm and wanting to get to that stuff without unzipping; all needs some space. The foot section and the hood are both lined inside with same material as the outside, which will help keep the down there dry from wet socks or snow covered hats. I was sent the regular length bag, but immediately noticed ME's 'regular' is noticeably longer than some other bags I've reviewed. Obviously making a bag shorter will make it lighter, but ME feel this can go too far and affect the usability of the bag. I always managed to lie down when using the bag, but for climbers bivvying on routes, the extra length will help if forced into nights sitting in the bag, not lying. I'm a little under 5'10” (176 cms) and there is loads of room for me.

The one minor annoyance I found with the bag was finding and using the popper that holds the draught collar closed. This is rather small, and doesn't seem to be where you think it is likely to be whilst feeling for it in the dark and cold. Making the two halves of the popper easier to find by perhaps surrounding them with a patch of material different to touch would help. It's by no means a major flaw to the design but annoying enough to stand out, perhaps just because everything else on the bags seems to work so well.


  • Total Weight: 1315G / 46OZ
  • Fill Weight: 800G / 28OZ
  • Max User Height: 185CM / 73"
  • Packed Size: 21CM X 33CM / 8" X 13"
  • Extreme Temp: -37°C / -35°F
  • Comfort Limit Temp: -17°C / 1°F
  • Comfort Temp: -9°C / 16°F
  • Good Night's Sleep: -20°C / -4°F

More info: on the Mountain Equipment Website

The other important thing that should be mentioned is that, like all ME bags now, the Snowline SL has a Down Codex number. This new system lets you trace back the down in your bag to the farm it came from, and the system is designed to guarantee animal welfare. I'm not a vegetarian but, like most people, wish that there is not unnecessary suffering involved in producing my food. The Down Codex system ensures this for down production and ME should be commended for considering the ethics of their products, not just the technology.


So, in conclusion? There is no getting away from it, a top of the range sleeping bag like the Snowline SL is a lot of money, but it's not the sort of thing that anyone would buy on whim: you'll know if you need something that provides such high levels of warmth allied to such a low weight. What I can tell the potential buyer is that, from my experiences of sleeping in it at -20 and colder, the Snowline is warmer than Mountain Equipment say it is and all the more remarkable a piece of cold weather equipment for that.

-22.7  © Toby Archer
© Toby Archer
The Drilite Loft SL fabric keeps snow and moisture out; here frost crystals from frozen breath.  © Toby Archer
The Drilite Loft SL fabric keeps snow and moisture out; here frost crystals from frozen breath.
© Toby Archer

Marmot Genesis softshell jacket: Toby ice climbing in North Wales  © Toby Archer

About Toby Archer

Toby is based in Finland. He describes himself as: "a writer and researcher specialising in international security politics; finally no longer a PhD student; hopeless but enthusiastic climber; part-time gear reviewer; keen multi-role cyclist; idealist and cynic"

Climbing keeps him from getting too depressed about politics. He blogs about both at:

Light from the North - chilled thoughts from the top of Europe.

For more information visit Mountain Equipment/Snowline SL

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29 Mar, 2013
I wish all UKC Reviews were this informative, comprehensive and well written. The -15C/-17C area is a bit lacking in bags, I've found. Plenty of good bags on either side but no standouts around that particular spot. Might make a good expedition bag for all but the poles.
29 Mar, 2013
//' title='Mountain Equipment - /the_gear/sleeping_bags/extreme_sl/ligh...'> might well hit the mark you mention of about -15. I was also rather impressed with the Sea2Summit bag I reviewed a couple of winters back which also is good to -15 Although it's only a 50 grams or so lighter than the Snowline and I remember on one -15 night my thighs were a touch cold by morning (wearing some fleece troos would have sorted that). The thing with the S2S bag is that they have this clever design to make it work better for continuous use, with the synth outer layer. Unfortunately though I haven't had chance to do multiple nights in a row in either bag - two was the limit - to see whether the S2S construction keeps the bag going for longer. It would be really quite complicated to create "controlled" situations to test that, but if it does work I could see the slight weight increase being justifiable for expedition use.
29 Mar, 2013
The S2S bags look good, but they're expensive and I've never found a place with a few different models all together to compare them in the flesh. My comment re: "might...expedition bag" was because I find choosing a bag to take on non-antarctic trips one of the hardest gear choices. I used a Rab Premier 900 for many years, which was a great bag. But as a BC bag on the Gasherbrum Glacier at 5000m, supposedly -10/-15C, I got cold several nights over the course of a couple of weeks. But the same bag for a few nights at 5300m on Ausangate a couple of years ago, around -15C, I was fine. So often on expeditions you are not feeling 100% and have not eaten well, so your body is not generating heat and sleeping like normal. And different locations, though numerically the same (eg. 5000m/-15C) can feel quite different. At Kula Kangri BC, around 4500m(?) in Tibet, I used a $50 KTM fake 'Marmot' bag rated around -5C and felt fine. That same trip I used the Rab 900 at 6200m and bloody froze (-20C?). These places can have such extremes, so hot in the day and then surprisingly cold at night, you feel like an idiot packing a -25C bag on a mule in 30C heat, which you then lay over your tent (the bag, not the mule) at midday at 3500m because it's so hot inside. Then you have to carry the thing. You know that it might get to -30C at a high camp, but buggered if you're going to carry a polar size bag up that high in a climbing pack. So you want lighter/smaller - but how much smaller? Wear more clothes inside? Hmm, not always great. So you plan to suffer a bit - but how much, and for how long? So a good light bag in this -17Cish range can be useful. As you say in the review, -20C is serious. Around -5 to -10 maybe you can tough it out for the night if you muck up your bag choice, or just don't care. But at -20 you might not make it through the night, at least not in any shape to go on. Around -38C things start to get weird, but that's for another time... :-)
29 Mar, 2013
Gulp... :( I've slept out in temps we've clocked at -27 a few times, for few days in Lyngen where I was using my friend's ME Iceline, which back then (mid-90s) was rated to about -25 I think. It was superb, and shows that ME have been doing this sort of kit for a long time and know their stuff. The second time was in central Finland in Buffalo 4s inner and outer, which I reckon might have been good to -10 absolute maximum. That was not a great night and I remember it in a lot detail still 15 years or so later! The stupid thing was (in retrospect) that we were essentially car camping, and my Finnish mate had brought his sleeping bag and then just the duvet of his bed to put over that! Not sure why it didn't occur to me to bring more layers. Was just looking at ME's new website section for the new bag ranges. Their Extreme range looks mental, three models with a good night guarantee for -50, -40, and the lightest ones say -40 too although I suspects that's a typo and it should be -30. The idea of sleeping at -50 seems... well... I can't really imagine what that could be like.
29 Mar, 2013
hey toby, im going to rate this as your best review yet. very dense in the sort of data a review should have, lots of 'surround data' (mats, keeping gear warm etc). quality. i will differ tho with your comment re double bagging (one down + one synth). for the weight i think the combo equals or surpasses that of a single at the same warmth and function (even with all the extraneous fabrics and junk that a double system includes). having been a user of doubles for 4 winters and several expeds (in temps same as you) i will happily qualify 2 bags weighing 550g and 750g each going to -28c. and the outer being a cheaper racing bag (by isuka). have used this same combo now for about 110 nights, and it functions as well in serious cold as it does in humidity (either atmospheric or from steam in a tent). dont get me wrong, im not trying to poke holes in your review - rather the industry that seems to ignore what many clmbers know and do. double bags also eliminate the cold patch issue behind the zip baffle, along with a demand for hi-tech (& expensive) baffling methods, and function aross a much larger temp spectrum (a true exped function). as a sleeping-system-obsessive your review here presents much needed real world data that is usually missed in s/bag reviews (that the likes of damo has got involved shows a standard in its own way). great to see, and i hope youve stirred up interest in the way bags, insu gear and general stuff gets presented. just 2 more things: 'yurt' is a russian word of altai origin and considered offensive in central asia/mongolia. pedantic i know, but a big deal thereabouts for ethnic reasons. and tallisker: good choice.
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