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(The Gear Loop) - We won’t beat around the bush, the concept of wild camping in winter can feel very bleak. Add in the idea of pitching a tent up a mountain, where the temperatures can plummet far below what any sensible person would consider comfortable, and you’ve potentially got yourself a recipe for disaster, let alone a bad night’s kip. 

However, with the right gear, the experience can be incredibly gratifying, awaking to glacial views and stunning vistas, all while remaining toasty warm. Alongside a good quality winter tent to keep out the worst of the weather, a very warm sleeping bag is the most crucial piece of kit if you want to comfortably wild camp. 

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With that in mind, you won’t find the sleeping bags featured on this list thrown in with the pop-up tents and neoprene roll mats at your local supermarket, because they are highly specialised and technical pieces of kit that the hardiest adventurers rely on to stay warm (and alive) when out in the wild.

All the bags reviewed and tested will keep you cosy when the mercury plummets to -9°C outside, and some will handle event more extreme temperatures, with ratings that see them handle a chill factor as low as -18°C.

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You might not be negotiating the side of Everest this winter, but that doesn’t mean one of these bags isn’t for you. The decent comfort level spread should keep things perfectly toasty throughout a range of temperatures.

And for anyone thinking they won’t be needing a bag that’s rated down to -40°C, the coldest night on record in the UK was -27°C in Scotland in 1982. Add in windchill factor in exposed areas and you’d be surprised how frosty things can get.

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Due to their ability to be used in hostile environments, all of the bags listed are what’s referred to as "mummy shapes". The tighter cut around the body to reduces the volume of dead space, which will trap warmth faster and will better maintain the perfect temperature. 

In terms of insulation, only one of the bags on test forgoes duck or goose down in favour of a synthetic insulation. It’s commonly accepted that down is warmer pound for pound, as our insulated jackets article found, but synthetic fill can survive a soaking and dry out much faster than its organic counterparts. We’ve got some more in-depth information on how to choose the right sleeping bag for you at the bottom of this article.

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The best winter sleeping bags

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Rab Ascent 700

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For

  • A hugely popular cold climate bag
  • Dry bag stuff sack
  • Larger sizes available

Against

  • Not as warm as others

Take a straw poll of brave folk sleeping up mountains on any given evening (granted, a very niche survey) and you’ll probably find a good number of those are tucked up in the British stalwarts’ Ascent 700 bag. 

Filled with 700g of certified European duck down, this bag kept us warm when the temperature dipped to around -8°C on a chilly night in the Highlands. 

The down used, however, isn’t the warmest available in the Ascent line-up, so if you’re planning an epic winter adventure, the Ascent 900 might be a better purchase. But the benefit of using a slightly less fluffy down is that the bag packs into a surprisingly small and lightweight package, which is great when your pack is already overflowing with food, a stove, coats and the normal camping necessities. 

The stuff cask included is actually a roll top dry bag, which is a really nice touch to make sure the sleeping bag doesn’t fall victim to any moisture. A plethora of toggles and zippers allows the fit to be tailored to all body shapes and sizes, while Rab even offers an XL model with an extra 15cm of length to accommodate the taller members of the outdoor community. 

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Snugpak Softie Expansion 5

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For 

  • Employable side baffle
  • Very warm

Against

  • Synthetic down used
  • Stiff construction
  • Heavy

Snugpak is an independent British brand that has gained a reputation for designing and producing great quality sleeping bags at a very competitive price. The Expansion 5 is no different, because in our eyes, £146 for a bag rated down to -15°C  is a bargain. 

A large part of the cost saving is down to the use of synthetic "Softie" fill, which Snugpak claims involves the use of, "superfine yarns with special resins to create a luxurious down-like feel". After testing for a week or so, the difference between this and natural down was fairly obvious, as it was noticeably stiffer when trying to stuff it back into its carry bag. 

Handily, Snugpak has included a deployable side baffle, which can provide a little extra room for those with broad shoulders or to keep smaller campers cosy. Unfortunately (or fortunately, depending on how you see it), the temperatures didn’t plummet sufficiently to comment on the warmth in the biting cold, but in low single figures, it kept us toasty with the added benefit of drying extremely quickly after getting soggy attached to our rucksack. 

The biggest pitfall here is that the Expansion 5 is a weighty beast, tipping the scales at 2.3kg. It also doesn’t pack down particularly small, which could be a deal breaker when space is at a premium

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Kelty Cosmic Ultra

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For

  • Waterproof down treatment
  • Internal pockets
  • Comfortable

Against

  • It’s huge
  • Pricey

Hailing from the USA, the Kelty Cosmic Ultra is the warmest bag on test here, comfort rated to -18°C, mostly thanks to 1000g of 800 FP (read: very fluffy) DriDown down that has been treated with a molecular level polymer to create a hydrophobic finish to each feather. 

It sounds complex, but in practice the down will stay drier and loftier than untreated down and will also dry faster should it get wet. Kelty claims that over an eight hour period, an untreated bag will lose 30 per cent of its loft, transforming a -10°C capable bag into a 0°C bag, which is a substantial loss. 

DriDown claims to retain 98 per cent of its loft, which should keep you warmer for longer. The downside to having 1kg of very fluffy down is that even when compressed into the stuff sack, there’s no escaping the fact that this is a humongous bag. It’s also the most expensive on test, but is designed for the most extreme conditions. 

Internal pockets for storing thing, an ultra-soft inner lining and a general design that leans heavily on the comfort factor means this bag scores top points from us, it’s just a shame it takes up so much room.

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Nemo Disco

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For 

  • Great for side-sleepers
  • Weatherproof and breathable footbox
  • Pillow pocket

Against

  • Not the warmest bag on test

Another sleeping bag from across the pond, the curiously named Nemo Disco is a feature-rich offering at an excellent price. The most striking difference between the Nemo and the other bags on test is its shape. Mummy bags have become de rigueur among those wanting the peak of performance, as it reduces excess volume. 

However, if you’ve ever tried to sleep on your side in a mummy bag, you’ll know it’s not an ideal situation. Enter the Disco, which has been designed for side sleepers; utilising a unique spoon shape, it adds room at the knees and elbows to allow for a bit more wriggle room, which was greatly appreciated by this guinea pig. 

An array of technical materials are deployed tactically around the bag to provide even more comfort. The waterproof and breathable footbox was a welcome addition, as it meant our feet stayed warm and dry without becoming sweaty. The space-age sounding Thermo Gills were great at keeping us at a perfect temperature when things got a little too toasty. 

Perhaps the most heralded feature  during the test was the pillow pocket: essentially an area where you can stuff soft items - or Nemo’s own Filo pillow - to offer five star levels of comfort. Even the zip is clever, as it features a small plastic shroud to prevent things getting caught and jammed, which can be very frustrating when dealing with cold hands and potentially fragile sleeping bag shells.

It was also the lightest bag on test, but that’s because it didn’t pack the same fill power as others, meaning it is rated down to -9°C. This should cover off most scenarios for most people, in which case, it’s a fantastic bag. 

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Alpkit Alpine Dream 800

For

  • Huge fill power figure
  • Extremely warm
  • Lightweight and packs small

Against

  • Non-traceable down
  • Lacks eco credentials

Alpkit is another UK-based brand that has been providing top quality kit to serious outdoor enthusiasts for years. The Alpine Dream 800 carries on this tradition, offering 800g of 750FP down spread over 13 baffles to fend off temperatures down to -15°C. 

The bag is nowhere near as feature-rich as some of the others on test, using untreated Chinese goose down and a traditional mummy shape, but it weighs just 1300g and at a competitive price, there’s not much to grumble about.  

On test, it was perfectly warm enough during our Highlands camping trip and its small pack size made it one of the easiest to lug around. Comfortable, too, just not as extreme as some of its chunkier rivals.

What’s more, Alpkit vows to repair or replace the product under their Alpine Bond scheme should your sleeping bag get ripped or torn out in the field.

Alpkit is sold exclusively through its own website, the Alpine Dream 800 costs £279.99.

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What to look for in a sleeping bag

Become a seasoned pro

Sleeping bag warmth is measured in two ways. Firstly, there is the season rating, which should be reasonably self-explanatory, as it loosely describes how many seasons of the year the bag will be suitable for. Starting at 1 season, these bags are great for a summer camp out where the temperatures are reaching mid-single figures, 5 to 8°C. 

Upgrade to 2 or 3 season bags and these will keep you warm during colder nights when there’s no frost. Above this, 4 Season bags are suitable for a cold winters night, down to around -10°C. Sitting at the top of the pile are 5 season bags, which are designed for the most extreme conditions when temperatures can get down to -40°C. 

Are you sleeping comfortably?

The second rating system is dubbed the comfort system. Typically displayed as both the comfort and extreme temperatures the bag will happily operate in. This gives an indication as to the temperatures an average person will feel comfortable in the bag. 

The extreme rating denotes the lowest temperature an average women could survive in the bag for without receiving life changing injuries from the cold. Throughout this article, we referred to the comfort temperature, rather than the extreme, as it simply wouldn’t be a comfortable night at all if you were running right up to the extreme temperature limits.

Feel the fill power

Like insulated jackets, sleeping bags also receive a fill power rating, which essentially denotes the amount of down or synthetic insulation that lives inside the bag. The higher the number, the more space 1g of down will take up, typically indicating the down is of better quality and lofts - or fluffs - with greater ease. It’s also worth considering that higher fill power also tends to mean more bulk, which can add a lot of size and weight to your trekking pack. 

Writing by Matt Buckley. Originally published on 1 December 2021.