Stay snug outdoors when temperatures plummet: Our experts pick the top winter sleeping bags of 2025

Therm-a-Rest makes some of the best sleeping bags on the market and the superb Parsec -18°C is no exception. It is warm, cosy, light, very packable, fully featured and quite eco-conscious – it ticks all of the boxes.

With a -10°C comfort rating but clocking in at around 1kg (excluding compression bag), it offers a phenomenal warmth-to-weight balance. This is achieved through clever ‘heat-mapped zoned insulation’. Most (70%) of the down in the top of the bag where you need it most, and 30% below your body. Hence the Parsec is able to deliver better temperature ratings at a similar weight to competitor products – a massive win.

Other features include a 100% recycled ripstop nylon DWR shell and liner, and ‘synergy link’ connectors that strap your bag to your mat for an integrated sleeping system. The Parsec also has a super-cosy ‘toe-asis’ footbox, and heat-trapping draft collars and baffles. Compression and stuff sacks are provided too.

Regarding niggles, we wonder about the long-term durability of this bag’s lightweight construction – will it cope well with prolonged heavy use in the outdoors? Also, the premium price will be prohibitive for many, and the temperature ratings may be overkill for milder winter camps.

The Kelty Cosmic Synthetic 0 offers a -8°C comfort rating for a very reasonable sum, although we found its -8°C comfort limit seems overly optimistic. But weighing in at 2064g, it's a nice balance for campers more concerned with price than the weight of their backpacks.

The mummy-style bag is filled with Kelty’s CirroLoft synthetic insulation, which feels thick and warm (there’s a whopping 1560g of it). It fluffs up pretty impressively despite being synthetic.

The polyester and nylon taffeta liner and shell, which Kelty describes as “soft as silk”, provide a cosy sleeping environment, and warmth is further locked in by a large neck baffle and insulated hood with drawcord adjustment.

You also get a spacious footbox, internal zippered pocket, PFC-free DWR treatment on the shell, compression stuff sack, and a ¾-length, two-way zipper with integrated baffle. In other words, you get a lot of bang for your buck with this bag. But is it too heavy and chunky for your mountain exploits?

As expected with cheap but very warm synthetic bags, the Cosmic is heavy and bulky, and therefore far from ideal for lightweight wild camping. The hood has a slightly odd shape too, and build quality and features are relatively basic.

The Sea to Summit Spark -18C is a premium winter sleeping bag offering exceptional performance. With 840g of 850+ fill power goose down, it creates a thick, warm cocoon rated to -10°C (comfort) and -18°C (comfort limit).

Weighing just 1,255g and packing down compactly, it boasts an outstanding warmth-to-weight ratio ideal for serious winter campers.

Key features include ethically sourced hydrophobic down, an adjustable hood, a cosy footbox, and a smooth ¾-length two-way zipper. However, the ultralight 10-denier fabrics feel delicate, and the mummy cut might feel restrictive for some.

At £625, it’s a significant investment, and potential issues like down migration may arise over time.
While pricier than competitors like the Simond Makalu III, the Spark -18C excels in weight-saving warmth. For those venturing into extreme cold, it’s a top-tier choice that delivers where it matters most.

Rab’s Neutrino hand-filled sleeping bags are always a safe bet for quality and performance. There are 10 products, each filled with 800 fill power goose down. The fill weight, however, increases in 100g increments from 200g to 900g.

Eight bags are unisex, the 400 and 600 are available in women-specific versions too, and the 300, 500, 700 and 900 are ‘pro’ versions with a more weather-resistant Pertex Quantum Pro shell.

We’ve tested the third warmest option – the Pro 700, which features a highly-tapered mummy design, good warmth-to-weight ratio, and strong weather protection. With a 700g fill weight, the bag is toasty (-4°C comfort rating), and the shell feels reassuringly rugged too.

Weight-saving, chevron-shaped baffles allow the down to fully loft, eliminating cold spots and maximising warmth. Additional zipper and neck baffles further lock in warmth.

You also get an adjustable hood, ¾-length YKK zipper, angled footbox, cotton storage sack and waterproof compression sack. The shell and liner are 100% recycled.

The tapered cut might not suit all body shapes, so try before you buy. The price tag is sky-high and only justifiable for serious winter campers, and the -4°C comfort limit is disappointing considering the cost. If the insulation was zoned better, the temperature ratings might improve.

Check out the Long version here

You can easily spend an absolute fortune on a down winter sleeping bag. But to save hundreds of pounds, instead opt for a synthetic sleeping bag from a price-conscious brand like Scottish firm Highlander.

The mummy-shaped Serenity 450 offers superb -4°C comfort and -10°C comfort limit ratings, courtesy of two 225gsm sheets of flat, wadded synthetic insulation.

The shell is a 210T ripstop polyester and the lining is a 210T polyester pongee. Features include an adjustable thermal hood, cinchable shoulder baffle, Velcro storage pocket for a phone or headtorch, and a two-way, ¾-length zipper with an integrated baffle.

All-round comfort is more than adequate considering the price. But ultimately, this is not a premium offering for winter camping connoisseurs. Instead, it’s squarely targeted at occasional winter campers and bargain hunters, who don’t mind the extra weight and bulk.

Weighing in at 2065g, it’s very heavy, as well as bulky and chunky, so it takes up lots of space in your backpack. The overall build quality is relatively basic and cheap (as expected at this price). The polyester lining isn’t the comfiest, and the shell feels too loose and detached from the insulation.

The Thermarest Saros 0F is a great value synthetic sleeping bag, ideal for beginners and budget-conscious campers. Priced at £225, it offers solid performance with a -10°C comfort rating and -18°C comfort limit. Weighing 2,408g, it strikes a balance for those prioritizing affordability over pack weight.

The bag uses Thermarest’s EraLoft polyester hollow fibre insulation, packing 1,820g of thick, warm fill that lofts impressively for a synthetic option. Its roomy, relaxed fit features the WARM (With Additional Room for Multiple positions) cut, making it particularly comfortable for side sleepers or those who move during the night.

However, the Saros is bulky when packed and relatively heavy, which might deter weight-conscious backpackers. Despite this, its reliable warmth, durability, and user-friendly design make it an excellent choice for cost-effective cold-weather camping.

Sitting firmly in the mid-range of the market, the mummy-style Robens Couloir 750 is a great all-round package. It's warm, well-designed and fully featured.

The insulation is 750g of 700 fill power responsibly sourced duck down, providing an accurate and impressive -8°C comfort rating. That said, lighter bags are available with similar temperature ratings.

The standout feature of this bag is its central zip. It may polarise opinion, with some potentially finding it awkward for comfort and venting. But we found it makes getting in and out easy in a cramped tent.

It also lets you finely control ventilation and adds versatility (completely unzip to use the bag like a quilt). The central zip also enables you to sit up in the bag and use your arms for chores like cooking or gear organisation.

A humongous double baffle underneath the central zipper eliminates heat loss. Warmth is sealed in further by the adjustable 3D hood and super-cosy ‘thermocollar’. This is a plush baffle of down providing a snug fit around the neck and shoulders.

You also get a ‘shark fin’ footbox, body contour profiling, hanging loops, mesh storage sack and compression bag.

The OEX Leviathan EV 900 is an exceptional bargain for a four-season down sleeping bag, costing just £169 with a £5 Go Outdoors membership. It boasts impressive temperature ratings of –9°C comfort and –16°C comfort limit, though these may be slightly optimistic.

Still, it’s warm enough for sub-zero camping near freezing, thanks to 900g of 600 fill power grey duck down.

The bag’s mummy-style cut is lightly tapered but not overly restrictive, offering a good balance of space and warmth. Key features include a ¾-length zipper, a snug neck baffle, and a well-designed hood. Weighing just 1,399g and packing down compactly, it’s highly portable.

The downsides? The 600 fill power down lacks the loft and insulation of higher grades, and the build quality feels basic compared to pricier models. However, for its price, the Leviathan EV 900 delivers excellent value and reliable performance.

The Rab Alpine 800 is a great option for those seeking a winter sleeping bag from a trusted brand without a £500+ price tag. Priced at £330, it offers solid features, clever design, and good warmth-to-weight performance.

The bag uses 800g of 650 fill power down, which is ethically sourced and treated with a Nikwax hydrophobic coating. While not the highest-grade down, it provides reliable warmth for sub-zero temperatures, though we wouldn’t recommend it for anything below -10°C.

Rab’s in-house Sleep Limit of -16°C is based on real-world feedback rather than EN/ISO testing, but it’s roughly equivalent to a ‘comfort limit’ rating. The bag includes a weatherproof Pertex Quantum shell, an adjustable hood, a cosy footbox, and chevron baffles for even down distribution.
Though it lacks the thick loft of premium options, the Alpine 800 delivers excellent value and performance for moderate winter conditions.

Although the Exosphere –10 has been replaced by the Exosphere –11 for 2024, we still recommend the Exosphere –10 if you can get your hands on one, purely because of the 'last season' value it offers.

This bag gives you a -4°C comfort rating, lots of features and a good all-round design for an agreeable price.

The fill is deuter’s Thermo ProLoft synthetic insulation, which feels warm and cosy, while the overall design is best described as super-stretchy.

It features internal and external elastic chamber seams, which provide 25% expansion and contraction in the bag’s width. This means the bag stretches with you as you move at night, but when you’re still the insulation is close to the body, eliminating cold spots and making it super-snug.

Other nifty features include the use of brushed fleece inserts inside the bag for a lovely soft feel, extra water repellency at the head and feet via a sturdier Dryzone shell, and Velcro closure to the adjustable neck baffle for a sealed-in feeling around the head.

You also get an adjustable hood, full-length two-way zipper, added insulation in the cosy footbox and a compression sack.

If you’re going for a budget synthetic bag, there are far cheaper options out there. It’s pretty heavy and big, even when compressed down, and some will find the body-hugging sensation far too tight, narrow and constricting.

Check out the Long version here

Decathlon’s Simond Makalu III delivers exceptional value for a winter sleeping bag, priced at just £290 ($365) with impressive EN/ISO ratings of -12°C comfort and -19°C comfort limit. Its standout warmth comes from 1,100g of 800 fill power duck down—200–300g more than many competitors—providing a plush, thick loft for excellent insulation.

Designed with an alpine focus, it features a tapered mummy shape and a central half-zip. While the snug fit enhances warmth, it may feel restrictive to some. Weighing 1,814g and packing down to 40 x 27cm, it’s slightly heavy but manageable for winter adventures.

Though the down isn’t hydrophobic and the eco credentials could improve, the Makalu III’s performance and affordability are hard to beat. Comfort levels are generally good, though the interior’s shiny, plasticky feel might not suit everyone. For serious cold-weather camping on a budget, this is a top-notch choice.

The Alpkit SkyeHigh is a no-frills winter sleeping bag with a classic design and all the essentials expected from a four-season option. Its standout feature is affordability, priced at just £250 ($315), delivering solid mid-range performance.

Warm and comfortable, it includes an adjustable hood, cosy footbox, and a ¾-length two-way zipper. At 1,541g (with stuff sack) and packing down to 35x22cm, it’s also compact and portable.

The cut is moderately tapered but roomier than most mummy bags, appealing to campers who prefer extra space, though some may find it less efficient in retaining warmth. The 650+ fill power duck down (900g fill weight) isn’t hydrophobic and is average quality, but it’s typical at this price.

Rated to -6°C comfort and -13°C comfort limit (EN/ISO), it’s warm enough for most winter conditions, though not the warmest in its category. Some components feel basic, but overall, it’s excellent value.

This nifty sleeping bag liner is soft, stretchy, and super comfortable. Yet, it adds considerable warmth to your sleeping system (up to 8°C) while being much lighter and compact than most thermal sleeping bag liners.

Highlander is popular among hikers for the value it brings to the outdoor gear market. While the Sea to Summit liner is the better performer, this snug fleece liner is a great alternative if you're on a budget.

Bluesign-approved, PFC-free, and water-based, this is a sustainable and effective wash for down and synthetic-insulated sleeping bags, gear, and clothing. It's a concentrated formula too, so a little goes a long way.

Like Grangers, Nikwax Down Wash Direct is an eco-friendly and effective cleaner for all insulated gear. This kit also contains Nikwax Down Proof, which revitalises water repellency.