Chris Kempster tries out a down sleeping bag thats unbelievably light and warm... and great value tooReviewSpecsGalleryRetailersFounded way back in 1961 in the Peak District, Mountain Equipment, a brand beloved by mountaineers, mountain professionals and dedicated outdoor enthusiasts has always been known for having particular expertise in making cold weather products, and in fact down sleeping bags were one of the first products it ever produced. Since those early days, ME has stayed at the forefront of developments in the use of down, not just from a technical point of view, but sustainability too; it created the DOWN CODEX scheme in 2009, which allows consumers to trace the origins of the down in their clothing and sleeping bags, and since 2022 the DOWN CODEX program has been working alongside the Responsible Down Standard (RDS) to guarantee the highest animal welfare standards.MEs new Extreme Light range of sleeping bags consisting of the Xenith I, II and III models, is actually an update on the previous Fire models, which consisted of the Firefly, Firelite and Fireflash. There are plenty of improvements in the new range, which well come onto, but the concept remains the same to provide amazing warmth-to-weight performance. Most of the materials remain the same too, including the 900 fillpower 90/10 European goose down, and the PLASMA 10D fabric which, incidentally, is the same fabric used in Mountain Equipments Oreus jacket a firm favourite of team T&Ms.A combination of vertical box wall baffles on the chest, and slant (or V-tube) baffles elsewhere are usedExtreme LightThe three Xenith models largely follow the same warmth specs as the Fire models. The Xenith 1 (350) is a hoodless bag, ideal for alpinists who can pair it up with their puffa jackets for overnight bivis on ledges high up in the Alps; however theres nothing to stop lightweight backpackers taking advantage of its light weight (360g) and decent warmth rating (ME rates it on its Good Nights Sleep Temperature at 5C). The Xenith II (430) adds 110g and a hood, but now gives a Good Nights Sleep Temperature: 1C, which makes it eminently suitable for a wide range of trips, both in the UK and abroad. And finally the Xenith III itself, which for its 690g gives a Good Nights Sleep Temperature of -7C, and in MEs words makes it suitable for ultra-light backpacking and trekking in the high mountains during summer and at lower altitudes in spring and autumn.Got me baffledHow do ME achieve such impressive weight/warmth performance in their Xenith bags? Well the first part of the equation is the materials they use: in the case of the Xenith III, thats 373g of 90-10 European Goose Down with a minimum fill power of 900 (with the 90-10 meaning that at least 90% of the filling is down, with the remainder being feathers) this is among the best quality down available on the market. The inners and outers of the bags are made of PLASMA 10D, an incredibly light and breathable fabric that allows maximum loft of the down inside, and has a PFAS-free DWR coating to give some protection against damp.The second part of the warmth/weight equation is how the down filling is actually organised, and ME have used a combination of vertical box wall baffles on the chest, and slant (or V-tube) baffles elsewhere all with the aimof stopping the down from migrating, keeping it the right places. The footbox and hood on the Xenith III are again carefully designed to keep the insulation where you need it, and these are both areas ME say theyve improved on from the previous Fire bags.The supplied storage cube is a step up from regular storage sacksIn useWeve been using this bag for a few weeks now, and our initial surprise about how warm the Xenith III is for its weight has not diminished; the only comparable bags weve used are Rabs Mythic Ultra range. The Xenith III is certainly too warm for the summer months in the UK, but could easily be used the rest of the year, and would be ideal for trekking up Kili or in the Himalayas, for example. Although its light, you get a full-length zip thats sturdy enough for long-term use, and the hood is excellent, with a neck baffle to keep out drafts and giving you that cocoon effect that is so welcome when temperatures plummet. The alpine fit of the bag ensures there are no cold spots, but isnt so tight as to be restrictive. So far weve no gripes at all with the Xenith III and are looking forward to really testing it during some properly cold nights!SummaryTheres no doubting the quality and performance of these Xenith bags, and anyone wanting a down bag with exceptional warmth/weight performance should have these near or at the top of their list. The only quandary might be which model to go for! It all depends on what you are intending to use them for of course, but certainly the Xenith III we tested would suit a wide range of uses, from minimalist alpinism to backpacking and trekking in cooler temperatures, and for use in the UK in all but the warmest and coldest conditions.More info: www.mountain-equipment.comTemperature ratingsTemperature ratingsComfort-2C/28FComfort Limit-8C/18FExtreme-26C/-15FFeatures373g of 90-10 European Goose Down with a minimum fill power of 900PLASMA 10D fabrics throughout are incredibly light and breathable with PFAS-free DWRAlpine fit maximises thermal efficiencyVertical box wall chest baffles & slant main body bafflesSlant baffle backGround level side seams5 baffle low volume anatomically shaped hood4 baffle anatomically shaped and offset foot-boxFull length Gemini zip baffle with 140cm zip and integrated neck collarSupplied with roll-top stuff-sack and storage cubeFeatures373g of 90-10 European Goose Down with a minimum fill power of 900PLASMA 10D fabrics throughout are incredibly light and breathable with PFAS-free DWRAlpine fit maximises thermal efficiencyVertical box wall chest baffles & slant main body bafflesSlant baffle backGround level side seams5 baffle low volume anatomically shaped hood4 baffle anatomically shaped and offset foot-boxFull length Gemini zip baffle with 140cm zip and integrated neck collarSupplied with roll-top stuff-sack and storage cubeBuy online and in-store at:Ultralight Outdoor Gear