Mountain Equipment Xeros Sleeping Bag Review

Mountain Equipment have just released their new 2017 line of sleeping bags and there is quite an array to choose from. In this test we are looking at the Xeros, a sleeping bag designed for those wanting to go ultralight without compromising on warmth and comfort. It's a down bag that will be perfect for alpine climbing, winter camping in the UK or indeed anywhere that weight and bulk need to be kept to a minimum.


First and most importantly when it comes to sleeping bags, how warm is it? The Xeros has a rated comfort temperature of -5°C , a comfort limit of -12°C and an extreme rating of -31°C. But it also has a 'good night's sleep' rating of -14°C.

These figures require some context. In a recent article, Mountain Equipment's insulation expert Dr. Matthew Fuller explained how the standard comfort and extreme figures are obtained through the EN13537 test. While this is a useful standardisation across the industry, testing a bag's insulation ability in the real world is a complex business and the standard test does have its limits. Some brands also offer their own temperature rating, based on other methods of testing. This is where Mountain Equipment's Good Night’s Sleep Guaranteed figure comes in; it's a healthy -14°C in the case of the Xeros, which suggests that you may find this bag slightly warmer than the official EN13537 figures imply.

A great thing worth noting about the Mountain Equipment sleeping bag range, is that if you buy a bag and it fails to meet the required temperature then the bag can be upgraded through Mountain Equipment; terms do apply of course.

Being thin I'm not the warmest sleeper, so if anyone is likely to get cold it's probably me. But I've used this bag very comfortably within the comfort rating, roughly down to about -9 in the Alps and -4 in Scotland. Both times I had a very good night's sleep in only long johns, t-shirt and thin socks. I also had a night in Perthshire bivvying outside in this in light snow and light wind. Although this night probably would have felt the coldest due to windchill outside the bag, inside I was still warm and toasty..

Victoria not wanting to leave the Xeros in the morning  © UKC Gear
Victoria not wanting to leave the Xeros in the morning

Xeros at Plan de l'Aiguille  © UKC Gear
Xeros in the Alps - freezing outside, toasty in the bag

Weight wise, I make the Xeros to be 1095g which for a bag rated to these temperatures is excellent. And with the Xeros in its stuff sack I've been able to get its volume down to roughly 26cm x 24.5cm x 22cm. This modest weight and pack size for the amount of insulation on offer is really what's going to make this bag great for alpine climbing, where every gram and every bit of space matters. Of course it's not just cutting edge alpinists that stand to gain from a bag of this calibre; if you're prepared to make the outlay then it'd be welcome lightweight warmth for any mountaineer or winter backpacker.

Fit and Features

The Xeros comes in two sizes - Long and Regular. For this test I've been using the Regular. The cut of the bag is what Mountain Equipment call an Alpine fit. This seems to be a narrower fit, and really cuts down the amount of air your body needs to heat. It also has the added benefit of reducing the overall volume to pack.

A noticeable feature when moving around in the bag is the elasticated stitching within the lining, referred to as EXL technology. This basically keeps the bag snug against your body, eliminating dead airspace and helping the down within the bag to loft. It’s claimed that this alone adds around 2°C to the rating of the bag. I really like the way this elasticated stitching pulls the bag in to your body. It's just very comfortable and really feels like you are protected from the cold outside.

Like other Mountain Equipment sleeping bags the Xeros uses a Trapezoid baffle construction with overlapping seams, resulting in fewer cold spots and greater thermal efficiency. Think of these like a series of wedges instead of just rectangular blocks that hold the down. You might not spot these immediately since they are what make up the internal structure of the bag, but you will notice that the both inside and outside the bag there is a recurring large and then small baffle - the small baffle being the narrow edge of the wedge, and the large one the wide edge.

For sealing in the warmth, Mountain Equipment have added a neck collar which closes with little magnetic studs. Running along the zip is a full length baffle to keep draughts at bay. Around the hood there is a draw cold that can be operated with one hand to be fully drawn in, so that only a small breathing hole remains in the hood; the fit around the head is really snug.


Inside: The down - it's the key ingredient. Not skimping on quality in the least, the Xeros contains 605g of 90-10 Russian Goose Down with a minimum fill power of 800. For those unsure what these numbers mean, 90-10 is quite simple. The bag contains 90% goose down (the fluffiest stuff) and 10% goose feathers. Fill power is the key value that you should look out for when buying a bag. It’s the measurement that determines how well the down lofts (how much air the down can trap). The higher the fill power value, the greater the volume of air a single gram of the down can trap and as a result, the warmer the sleeping bag will be for a given weight of fill. As a guide 400-500 is considered medium, 500-600 is considered good, 600-750 is considered very good, and 750+ is considered excellent.

Victoria in the Xeros  © UKC Gear
The hood gives a close seal around the face

Water beading on the Xeros  © UKC Gear
Water beading on the Xeros

After removing the Xeros from the compression bag the down lofts well, probably in part due to the elasticated stitching. I usually give it a bit of a shake and lay it flat for a moment to get it going. I've slept in the bag around 15 nights now and after this use the loft still seems as good as new. Look after it well and a bag of this quality should offer many years of reliable service.

Outside: The outer is constructed using Mountain Equipment’s DRILITE Loft XERO 10D. At only 10 denier, this material basically sets out to be lightweight while being able to stand up to a reasonable amount of wear. Heavier versions of it are used on many other of Mountain Equipment’s down insulation garments too. The material provides a hydrostatic head of 1500mm yet is still breathable. This level of water resistance is enough to keep light snow and condensation from penetrating the bag and wetting the down. It's not going to stay dry in a rain storm, but you'd hopefully be in a bivvy bag or tent in that situation anyway. It does do a very good job of protecting the fill from condensation in a tent, which is a major bonus particularly if you're camping over several nights at sub zero temperatures, with limited ability to dry things out during the day. Over the last few months of use the outer on our review sample has stood up well, and there are no signs of wear on the material.


With superb levels of warmth for its surprisingly modest weight, the Xeros would be a great sleeping bag for anything from fast and light alpine climbing to UK winter camping. Materials, workmanship and of course the down fill are all of the highest quality, while the clever construction and feature set attest to the thinking that's gone into its design. Yes £460 is an awful lot of money; but how highly do you value a good night's sleep? A bag of this calibre is best considered a long term investment, and should offer years of service if looked after well.

Mountain Equipment say:

An ultra-light winter bag, ideal for those actively wanting to push the envelope in super-alpinism.

True expedition bags in all but weight, redefining what is possible for those in need of high levels of protection and reliable warmth. Developed specifically for climbers and mountaineers tackling the world’s last great problems and pushing the envelope of possibility to its limit, these lightweight, protective bags are anything but simple. Providing absolute confidence for selfsupported trips in remote locations, these are designed for alpinism’s leading edge.

Comfort: -5C

Comfort limit: -12C

Good night's sleep temperature: -14C

Extreme: -31C

  • Total weight: 1095g (our measure)
  • Price: £460
  • DRILITE® LOFT™ XERO 10D outer shell is ultra-light, highly breathable and water-resistant
  • 605g of 90-10 Russian Goose Down with a minimum fill power of 800
  • Alpine fit with EXL® system improves loft and maximises thermal efficiency
  • Trapezoid baffles throughout
  • Ground level side seams with V-side baffle
  • 7 baffle low volume anatomically shaped hood
  • 6 baffle anatomically shaped and offset foot-box
  • Full length Gemini™ zip baffle and integrated neck collar with Lode Lock™ closure
  • DRILITE® LOFT™ XERO 10D inner foot-box & hood lining
  • Supplied with waterproof roll-top stuff-sack and storage cube

For more info see

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1 May, 2017
I say - is he sleeping in his down jacket? cant be too warm then + the zips are very average!!
I had the zip partially down to allow movement while making a brew, so my torso was exposed to the elements.
1 May, 2017
A good night's sleep guaranteed my arse. Guarantee me a good night's sleep anywhere and I'll give you a million pounds.
1 May, 2017
And has to have a down jacket inside a £400+ sleeping bag?

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