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We tested 7 winter sleeping bags from some of the most in-demand brands out there to find the warmest and coziest options for your winter camping needs.
We have tested 60 of the best winter sleeping bags side-by-side over the past decade to find the warmest, most reliable options available. After purchasing the top-selling models, we spent the winter months camping in the snow and howling wind to evaluate their performance firsthand. From California's High Sierra to the rugged flanks of Maine's Katahdin, our team of ski patrollers, mountain guides, and seasoned adventurers put these bags through their paces.
Our top pick for most people is the Western Mountaineering Kodiak MF, thanks to its exceptional warmth, weather resistance, and lightweight design. If you're looking for something more affordable for frontcountry adventures, consider the Marmot Never Summer 0. Though relatively bulky, it balances impressive warmth with a reasonable price, making it a solid choice for most winter campers.
We rigorously assessed each bag's insulation, water resistance, weight, packability, and comfort, in the field and back at the lab to ensure accurate, reliable scores for each performance metric. Below, we share how each sleeping bag excels or falls short based on your specific needs, whether braving sub-zero alpine conditions or going winter camping in your car.
Editor's Note: We updated this review on April 24, 2025, to include new and retested models from brands like Mountain Hardwear, Nemo, and Feathered Friends.
Exceptionally spacious, lightweight, and comfortable even at temperatures slightly below its zero-degree rating
Beautifully constructed and incredibly warm, breathable, and compressible, this wonderful winter bag suffers from an excessively narrow cut
Offers warmth, comfort, and confidence heading into adventures, though you may need to size up
A great starter four-season sleeping bag option that weighs a little more but costs less than most
An excellent choice for cold-weather sleeping in dry conditions
If you prioritize water resistance and compressibility, this is a viable option, but its thin fabric, restrictive fit, and inconsistent insulation leave us out in the cold
A solid synthetic sleeping bag for mild winter conditions, offering impressive water resistance and reasonable warmth, though the narrow cut is somewhat restrictive
Weight: 2.8 lbs | Fill: 1.9 lbs of 850-fill goose down | Size: Reg
PROS
Super roomy
Wild warmth
Stellar warmth-to-weight ratio
Continuous baffles
CONS
Costly
Less hardy fabric
The Western Mountaineering Kodiak MF is an outstanding cold-weather sleeping bag that has earned a loyal following among serious adventurers. With massive 3D draft tubes and 1.88 pounds of 850-fill down, it not only meets but even exceeds its 0°F rating. Testers found that it seemed to radiate warmth and kept several of us warm in -10°F temperatures with a few extra layers added inside. A spacious cut, 67 inches at the shoulders, accommodates stomach, side, or back sleepers while making plenty of room for all the gear you need to insulate. It also packs down small and is impressively lightweight. Snag-resistant zippers and a comfortable, easy-to-adjust hood round out the package. It's our favorite balance of warmth, weight, and comfort for winter camping in the lower 48 states. Tester Jacob Holmes loved this one, among all options, saying, “I found it incredibly comfortable — like it's radiating heat.”
While extra space in a sleeping bag like the Western Mountaineering Kodiak MF adds comfort, it can also create uninsulated pockets of cold air. However, tester Clark Tate notes, “This is something I found easily mitigated by just stuffing a few of my extra layers inside.” Western Mountaineering bags set the gold standard among cold-weather sleeping bags, but are expensive. Care for it, and this high-quality model could last for decades. If you can't swing the high cost, we recommend the Nemo Sonic -20 bag, which is just as warm and a bit heavier for a more reasonable price point. The Feathered Friends Snowbunting won't save you any money, but the fabric is more puncture-resistant and weighs less for an excellent cold-weather sleeping bag.
The Nemo Sonic -20 is one of the warmest bags in the test, with a price tag that's only a bit above average. Considering how comfortable and versatile the bag is, it offers exceptional value. With 2.3 pounds of 800-fill down insulation, a well-tailored hood, and smartly placed zippered vents, it offers impressive temperature regulation across a broad range of conditions. Its performance in our field and lab tests gives us enough confidence to trust it in temperatures as low as -10°F. Testers also slept comfortably in temperatures as high as 40°F with the innovative upper vents unzipped and the main zipper slightly opened (though we don't recommend this if you sleep warm). The vents' ability to regulate your temperature, the water-resistant shell, and the hydrophobic down all help manage moisture in damp conditions. A cinchable face and neck gasket and a baffle to block drafts from the zipper round out the bag's thoughtful features. As tester Jacob Holmes put it, “It's amazing for cold nights! 100% I would buy the Nemo.”
This Nemo Sonic -20's streamlined cut holds warmth and saves weight, but it can feel restrictive for stomach sleepers, and tall sleepers may need to size up for a proper fit. Our 6'0" tester found the regular-size bag too short to be practical. At 3.7 pounds, it's not the lightest or most compressible winter bag we've tested, but it also has the lowest temperature rating in the review, meaning you're trading weight for a greater warmth guarantee. Like most sleeping bags, the soft, lightweight fabric requires careful handling to prevent wear and tear, and the included stuff sack is underwhelming. You'll probably need to invest in a higher-quality compression sack for backcountry trips. Despite these few complaints, testers never object to packing this bag for winter adventures, knowing they'll stay warm and dry in extreme conditions. And we love the price tag. If you don't camp in sub-zero temperatures, the Marmot Lithium is less expensive, fairly warm, lighter, and more compressible. If you just need a bag for car camping, check out the Marmot Never Summer 0, a more budget-friendly option.
The Marmot Never Summer 0 is a bright, fun, comfortable, and budget-friendly winter sleeping bag great for front-country camping in moderately cold conditions. Our testers stayed warm in temperatures down to 20°F in the field, and it earned average scores in our single-digit temperature tests. A handy internal pocket helps you stay organized. Still, the real benefit of this bag is its affordability, making it a solid choice for casual campers who don't need the warmest, lightest, most compressible bags on the market. One of its most comfortable design elements –- having two partial zippers, one on each side of the bag –- lets the top of the bag function like a cozy, blanket-like topper. The result is a more relaxed feel reminiscent of lounging on your bed back home. Tester Clark Tate explains, “When I'm car camping, I like to maximize comfort, and this bag feels more like a comforter than a mummy bag.”
Unfortunately, the dual-zipper design on the Marmot Never Summer 0 is less practical in the backcountry, where sleeping bags are essential safety gear. A full-length zipper is essential in an emergency where you must quickly tuck an injured person into the bag. All those extra zippers and less compressible, 650-fill power down also mean the bag isn't as light or packable as the higher-scoring options in the test, making it far less appealing to stuff into your pack. The large, roomy hood doesn't cinch down as snugly as higher-performing bags to hold in heat on frigid nights. Unless you have extra layers, this bag performs best at temperatures above the single digits. The construction quality is inconsistent, with some loose stitching and a flimsy stuff sack. Still, if you're looking for a good deal on a beginner cold-weather sleeping bag for car camping trips, this is the one we recommend. For a backcountry-friendly alternative, the Marmot Lithium is more packable and slightly warmer at a reasonable price. The Mountain Hardwear Lamina 0 is even less expensive, though it is heavier and doesn't pack down as well. It's also not as warm, but since it's synthetic, it can make a good option for warmer, wetter winters.
The Never Summer hood cinches down to a small opening, but it's not as smooth a process from inside the bag as higher quality options.
Credit: Clark Tate
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Our seasoned testers took these bags on winter adventures, like backcountry ski trips, to test their real-world application and performance.
Credit: Matt Bento
How We Tested
We scour the market for popular models from the most trusted manufacturers to discover the best cold-weather sleeping bags. Then, we purchased the top candidates at retail prices, just like you, and evaluated them side-by-side in the most extreme field testing locations.
Over the last decade, we've tested dozens of winter bags throughout the West Coast ranges, the Rockies, and the Northeast, bringing you diverse opinions and experiences. In February of 2023, we experienced record-low temperatures and high wind speeds on both Mt. Washington in New Hampshire and Katahdin in Maine — the perfect test environment. Since then, we've worked with professional guides who use a wide variety of gear while trying to maximize the quality of their clients' experiences. Their feedback — gathered from newcomers and seasoned alpinists alike — shaped our testing and informed our reviews.
Our cold-weather sleeping bag testing is divided into six performance metrics:
Warmth (25% of overall score weighting)
Moisture Management (25% weighting)
Comfort (20% weighting)
Construction Quality (10% weighting)
Weight (10% weighting)
Packed Size (10% weighting)
We compared sleeping bags rated from 0°F to -20°F, combining controlled experiments with real-world field tests. Our controlled testing involved measuring heat retention by carrying thermometers and relative humidity sensors into each bag with us and lying still for 20 minutes in temperatures hovering around 0°F. Field tests took place over multiple nights in sub-zero backcountry environments, where professional testers recorded comfort, fit, moisture management, and overall performance. We also assessed weight and packability to determine each bag's practicality for backpacking, and finally, we considered environmental and ethical certifications to ensure brands met high standards of responsibility.
By combining scientific testing with real-world use, we deliver reliable recommendations to help you choose the best winter sleeping bag for your needs, whether you're a first-time camper or a seasoned alpinist.
As you can see in the thermal images, the hottest areas in the sleeping bag appear in the brightest colors.
Thermal imaging makes it easy to see leaks when testing sleeping bags for heat retention.
We took thermal images of the bags during the temperature tests to check for cold spots.
Why Trust GearLab
This review is brought to you by Ryan Baker, Matt Bento, Jeff Rogers, Brian Smith, Clark Tate and Jacob Holmes. Ryan enjoys cozying up in the wilderness, from cold Sierra Ridges to frigid alpine glaciers of Alaska. He's traveled high and low as a mountaineer, skier, and climber through nearly every latitude and hemisphere. Matt has spent more of his life in a sleeping bag than he cares to admit, working in wilderness therapy and as a backpacking guide, and during his personal backcountry climbing pursuits. He's used roomy bags for weeks of living out in the snow and more lightweight bags for alpine missions in the Sierra. Jeff is an ambitious skier with many big ski descents under his belt, traveling everywhere from Alaska to Bolivia to pursue big lines. These adventures take him deep into the backcountry, where he appreciates a sleeping bag that is light and warm.
The Snowbunting proved super warm and cozy even under the coldest conditions.
It's important to dry out your bag well before storing it, if you want to ensure a long lifespan for your investment.
We tested these bags on the flanks of Katahdin, in the wintery wilds of Acadia National Park, and across the Sierra Mountains.
Brian is a licensed IFMGA/AMGA American Mountain Guide who puts gear through rigorous testing at home in the rugged Teton Range of Wyoming and on international trips. Clark is a former tent-dweller and van-lifer who has spent years without a traditional bed to crawl into. She put these sleeping bags to the test after winter surf sessions in Maine, on the flanks of Katahdin in Baxter State Park, and throughout the western Maine mountains and the frigid Atlantic coast. Jacob, a glacier researcher and winter mountaineering guide, leads winter ascents of Katahdin and has extensive experience helping clients endure nights in -20°F temperatures and below.
Analysis and Test Results
A key piece of gear in every person's overnight winter kit is their sleeping bag. Another way to think about it is as your survival capsule. If you accidentally rip a hole in your tent or break your leg miles from civilization, your sleeping bag would be the thin line between you and hypothermia. Luckily, most of the time, you'll just use it as a lofty down cocoon of comfort at the end of a cold day. On winter trips, when building a fire is challenging or wood isn't available, your body heat may be your only heat source.
We left each sleeping bag out in snowy conditions to test weather resistance.
We also documented warmth retention in frigid temps during testing.
And finally, we made side-by-side comfort comparisons of each sleeping bag in the snow.
Our rigorous test protocols include testing weather resistance.
Thankfully, modern down bags keep us alive and comfortable in the coldest conditions with waterproof/breathable fabrics, hydrophobic down materials, and clever design strategies. Shivering all night and surviving is one thing, but slumbering into a deep sleep to wake up refreshed is another. The ability to not only fall asleep but also rest and recover adequately is key to enjoying any skiing, hiking, or climbing you plan to do.
Our review selection includes bags that will keep you warm and comfy in the parking lot of your favorite winter crag and high-end, lightweight bags suited for climbing expeditions and backcountry ski tours. We brought back some tried-and-true favorites from our previous review and pitted them against various newcomers. We evaluated each bag for warmth, moisture management, comfort, construction quality, weight, and packed size.
Value
A key part of purchasing a winter bag is ensuring you can afford it. We don't factor value into a product's overall score to ensure an objective assessment of each bag's performance. Still, we understand that cost is a top concern for most buyers, so we address the issue here.
Less expensive bags tend to be heavier and filled with lower-loft down, leading to a heavier pack and a colder sleeping bag. If you won't be venturing into extreme, sub-zero winter temperatures, you don't mind sleeping in layers, and you're willing to haul a tad more weight, you can probably save a few hundred dollars or more. It's a personal choice, but one worth considering.
Also, think about the use case of this sleeping bag, being as realistic as possible. How often will you use this bag? Will it be a handful of outings or more like 30? A top-dollar sleeping bag may not seem expensive when you divide its price by a month's worth of nights out. If that's you, we highly recommend the Western Mountaineering Kodiak MF. Its superior warmth and comfortable cut will make it feel like a luxury hotel. The Feathered Friends Snowbunting is also likely to earn its keep over time, with durable fabric and insanely lofty and compressible 900+ down. On the other hand, its narrow cut isn't for everyone.
The soft, lofty, and warm Nemo provides a comfortable night in the winter wilderness for less.
Credit: Clark Tate
For those looking to balance cost and performance, the Nemo Sonic -20 is an outstanding value, delivering warmth, comfort, and innovative features at a reasonable price. The Marmot Lithium is the most reasonably priced bag for true budget hunters. It is warm, light, and compressible enough for winter backcountry missions, though we don't recommend it for extreme weather.
The Mountain Hardwear Lamina 0 also comes at a very attractive price. Though it's not as warm and packable as the other options in our review, its synthetic filling and water-resistant fabric make it a great option for warmer, wetter winters like those in the Northwest. The warm, cozy, yet heavy and bulky Marmot Never Summer 0 provides a great value for front-country winter camping.
The colorful Never Summer 0 isn't as light or warm as we'd like to cut it in the backcountry, but it's a great car camping option.
Credit: Clark Tate
Warmth
Several factors affect a winter sleeping bag's ability to keep you warm, including the type, quality, and amount of insulation, fabric thickness, the bag's cut, and features like the hood and venting zippers. Among bags with down feather insulation, the quality of the feathers makes a big difference. The quality is described as fill power, where higher numbers mean higher quality. Higher quality down is loftier, holding more air within more delicate feathers. This also means high-quality down is lighter and more compressible than lower-quality insulation. Good quality down is around 600 to 700-fill power, 800- to 900-fill-power is considered excellent, and 900+-fill power is the best of the best. The fill weight describes how much of the down is in the bag.
A Note on Sleeping Bag Temperature Ratings – While the International Organization for Standardization (ISO) has standardized tests meant to make sleeping bag temperature ratings comparable, they don't control which temperature ratings companies choose to advertise. As a result, advertised temperature ratings are not consistent across the board. Many companies advertise the lower limit for safe use, NOT the lower limit for comfort. Many 0°F bags are only rated to comfort limits in the teens, meaning that you may not get hypothermia in zero degrees, but you may find yourself shivering through the night. A common rule of thumb is to buy a bag that's rated about 20 degrees lower than the temperatures you will regularly experience.
A bag with a combination of high-quality fill power and high fill weight will have an exceptional loft, which will keep you warmer because it holds more insulating air between you and frigid air outside. Your body heat will warm those air pockets to create a cozy microclimate with your body heat. A roomier cut allows for extra layers and gear storage, which is very important because the only way to keep water from freezing and batteries from dying in the cold is to put them in the bag with you. On the other hand, larger bags are slower to warm up and can be prone to drafts. A bag that's too small could force you to compress the down surrounding the foot box, leaving you with cold feet.
Unsurprisingly, the bags that performed well in our temperature tests and kept us warm on frigid backcountry nights feature the highest quality down and lots of it. The Nemo Sonic -20 houses an impressive 2.3 pounds of 800-fill power down in the regular size and features a smart trim cut that warms quickly. Though Nemo claims it fits people up to 6 feet, our taller testers found they needed to size up to a long to keep their feet warm.
The Western Mountaineering Kodiak MF scored just as well in our warmth tests despite its higher temperature rating. The bag contains 1.9 pounds of 850-fill power down (in size regular), and the 20D Microlight XP shell seems to radiate your body heat back at you. We've found that Western Mountaineering tends to be conservative in its ratings, and we've used this bag in temps as low as -10°F with a light fleece blanket for extra insulation.
The Kodiak MF has one of the top warmth-to-weight ratios we saw across the lineup, providing a super warm, high-loft “nest” of 850-fill power down (1.9 pounds worth!) — this is one warm night's sleep.
Credit: Matt Bento
The Feathered Friends Snowbunting fared nearly as well in our tests as expected from its 1.9 pounds of 900+-fill power down. We tested the long version of this bag, though, as opposed to the regular size we tested in the Nemo and Western Mountaineering, leaving the Feathered Friend's bag with relatively less insulation per area. Still, the exceptional loft of its top-tier down is incredibly warm and cozy, even if the narrow cut makes it more challenging to fit gear that needs to stay out of the cold.
The less expensive Marmot Lithium and Marmot Never Summer 0 are a step down in warmth, with scores just a bit above average. The Lithium's 1.76 lbs of 800+-fill power down works just a bit better than the Never Summer's 1.97 pounds of 650-fill power down (both in a regular size). The trade-off is that the Lithium is lighter and more expensive. The 0°F rating on these bags is on the generous side. We prefer to use them in double-digit temperatures.
The Snowbunting ES slept warm in temperatures hovering around zero on a guiding trip in Baxter State Park.
Credit: Clark Tate
The thickness and quality of a bag's fabric also impact its insulating properties. The Mountain Hardwear Phantom 0 wraps you in 2.04 pounds of 800-fill power down but isn't nearly as warm as other options with similar specs. First, and most importantly, we tested this bag in size long, so the amount of down is spread across a larger area than the regular-size bags discussed above. Secondly, the fabric of this bag is remarkably thin, allowing you to clearly see the feathers underneath, which often shift to create cold spots. We tested this bag in zero-degree weather, and it was freezing all night. We wouldn't choose it for a night below 20°F if we could help it.
The Mountain Hardwear Lamina was only slightly warmer than the Phantom in our tests. As the only synthetic bag in the review, it doesn't compare directly to down bags, which are famed for their warm and compressible feathers. While synthetic fibers don't offer as much packability or warmth per weight, they do hold more warmth when wet than down does.
The Never Summer 0 is a go-to bag for winter surf trips in Maine.
Credit: Clark Tate
Moisture Management
Due to the variety of conditions you encounter while winter camping, a cold-weather sleeping bag must withstand some moisture. Condensation inside tents, moisture from your breath, and even light rain showers, mist, or melting snow are all realities your sleeping bag might face on a multi-day adventure. Sleeping bags have three lines of defense to avoid succumbing to moisture: 1. water-resistant fabric to keep moisture out, 2. water-resistant insulation to maintain warmth when damp, and 3. venting to reduce condensation in the bag.
To test the first two features, we used the bags on winter camping trips, dealing with condensation, spills, and drying gear along the way. We also tested them in the lab, leaving puddles of water on the interior and exterior fabric for 10 minutes to see how much would seep through.
The extremely lightweight 10D recycled nylon ripstop fabric with a DWR finish on the Mountain Hardwear Phantom 0 is remarkably water-resistant.
Credit: Clark Tate
The Feathered Friends Snowbunting, Mountain Hardwear Phantom 0, and Mountain Hardwear Lamina 0 all performed beautifully, with all of the water simply sliding off their fabric, which is treated with a durable water-repellent (DWR) coating. If any water had seeped through, the Lamina bag's synthetic filling would still have retained some insulating properties. Meanwhile, the two down bags wouldn't have fared as well.
Down, Hydrophobic Down, and Synthetic Filling – When down gets wet, it can lose its loft because the feathers collapse and can no longer trap air. In contrast, synthetic insulation retains warmth even when wet. Hydrophobic (i.e., water-repellent) down treatments help absorb less water, maintain loft and insulating ability even in damp conditions, and dry faster than untreated down.
Western Mountaineering disputes the effectiveness of water-repellent down treatments, instead arguing that feathers naturally contain oils that help maintain lofting when wet. This is a somewhat controversial stance. While birds secrete natural oils that they spread on their outer feathers to enhance water resistance, down itself is not an outer feather. Instead, it tucks beneath those water-resistant layers to keep the bird warm. There is also research that suggests that the waterproofing of outer feathers is more related to feather structure than to oils. (The oils condition the feathers to keep the structure from deteriorating.) In our experience, down does not work well when wet.
The Nemo Sonic -20 and Marmot Never Summer 0 performed nearly as well, with their water-repellent coating allowing some moisture to dampen the face fabric. Still, none of the water seemed to reach the down insulation underneath. If it had, the water-resistant treatment on the down in both bags should help them retain some loft.
While the Western Mountaineering Kodiak MF resisted condensation and mist in the field, and fallen snow brushed right off, it allowed most of the half cup of water we poured on the outer and inner fabric to seep through over ten minutes during our test. The down in that area was noticeably less effective as a result. Though the 20-denier MicroLite XP shell provides some water resistance, it isn't as robust as other options, so keep this bag dry. Only the Marmot Lithium provided less protection from water. It ran right through the fabric and insulation onto the floor.
We tested the weather resistance of these bags side by side in a range of conditions.
Credit: Clark Tate
Another important factor to consider is how well these bags ventilate or breathe. Everyone sweats in their sleep, though some more than others, and if you sleep with your mouth inside the bag, the moisture from your breath will dampen the interior. To combat this, winter bags often feature double zippers and cinchable collars that allow you to vent the bag while keeping your exhalations out of the main compartment. All the bags we tested include these features, though the Marmot Never Summer 0 has a less effective collar than most.
The Snowbunting's breathable panel helps keep you dry overnight. Using it in a lightweight, floorless mid-shelter on a winter backpacking trip reduced the risk of condensation on the face fabric, but this bag's water resistance would have worked either way.
Credit: Clark Tate
The Nemo Sonic -20 and Feathered Friends Snowbunting incorporate additional features to help you stay dry throughout the night. The Sonic achieves this by adding vents on the top of the bag that unzip to expose a single panel of fabric, allowing heat and moisture to escape. The Snowbunting, on the other hand, adds an orange panel of more breathable fabric (a 3-Layer Pertex Shield Air Panel) over your core. That fabric allows air to move through more freely when we back the bag, and, in our tests, the relative humidity levels remained lower in this bag, suggesting that the panel is indeed effective.
When we pooled water on each bag's internal and external fabric and left them for 10 minutes, the Laminia shrugged it off.
Credit: Clark Tate
Comfort
We judge comfort based on the feel of the bag against our skin, how much cushion and loft it provides, how the hood and draft collar fit, and how much space is in the bag. Sleeping bags with a wider cut generally received higher comfort scores. If you sleep exclusively on your back, a wide cut isn't as important, though you'll still have less space for your gear. The price of comfort is often more weight and space in your pack. Consider how well you perform after a poor night of sleep, and you may decide the extra weight is worth it.
The Western Mountaineering Kodiak MF is incredibly comfortable, with a silky liner and overstuffed baffles that make it feel luxuriously cozy. Its roomy cut (67 inches at the shoulder) accommodates side, stomach, and starfish sleepers without feeling claustrophobic, making it ideal for those who like extra space for gear or comfort. Testers like 6-foot-tall Jacob Holmes praised it as a “backcountry dream” for its spacious, cloud-like comfort.
The incredibly lofty Feathered Friends Snowbunting is equally inviting, and the ventilation panel helps you stay comfortably dry. Still, its narrow (though thermally efficient) cut makes it feel restrictive unless you sleep exclusively on your back. Similarly, the soft fabric and lofty down of the Nemo Sonic -20 are inviting, but its tailored cut can feel tight if you are at the upper limits of the size range. Though marketed for people up to 6 feet tall, our 6-foot tester found his feet pressed too tightly against the end, compromising insulation. Even our 5-foot-6-inch tester felt occasionally cramped.
One of our testing locations is deep in the backcountry.
The Western Mountaineering Kodiak MF and Nemo Sonic -20 kept two of our testers and their gear warm and cozy through the coldest temps we threw at them.
On a weeklong trip bunking in a three-sided lean-to in Chimney Pond, testers hunkered down through -10°F temps and a Nor'easter.
Both of these bags are especially tight around the knees, making it tricky to change socks inside. These bags are still very comfortable, and if you're interested either in alpine or big wall climbing, you'll likely be on your back anyway, sleeping on a narrow ledge or nestled among the rocks. Conversely, a thermally efficient cut can get tight quickly if you spend weeks climbing Denali or camping in remote and cold locations. With the added items needed to sleep with and the overall longevity of time spent in your sleeping bag, it makes sense to go with a wider cut like the Kodiak.
The Marmot Never Summer 0 offers a mixed comfort experience with a large hood and cozy blanket topper design, but a restrictive cut through the hips and knees. It works well in warmer conditions, but your leg movements are limited when zipped up for warmth. The tight fit around the knees also makes reaching your feet while inside difficult, which is crucial for tending to cold or injured feet. The expandable foot box doesn't do much and is more useful for ventilation than comfort.
The Marmot Lithium is well-padded with insulation, but its slim cut through the shoulders and hips makes it uncomfortably restrictive, even for slimmer users. The relatively thin insulation and narrow cuts of the Mountain Hardwear Phantom 0 and Lamina 0 keep them from winning any comfort awards.
The insane loft of the Feathered Friends Snowbunting makes it a welcome respite, though larger testers may struggle with the narrow fit.
Credit: Clark Tate
Construction Quality
After using these bags for months, we closely look for any wear and tear and test their fabrics, seams, zippers, and cinch cords to identify any signs of weakness. Feathered Friends' stellar reputation for quality construction is upheld in the Snowbunting ES 0 Degree, with sturdy fabric (15D Pertex Shield with 40D ripstop reinforcement and 3 Layer Pertex Shield Air Panel), stable stitching, an excellent zipper, and solidly constructed features. We expect this bag to last.
The rest of the bags are more prone to damage, and their lightweight face fabrics are relatively easy to puncture with the tip of a paperclip. For instance, the Kodiak MF's 20D MicroLite XP nylon shell is lightweight and wind-resistant but more prone to punctures than the Feathered Friends bag. So we keep a closer eye on it around crampons. While the Kodiak's sturdy metal zippers evoke an old-school feel, they occasionally snag the fabric, and the bag's exposed stitching can cause the fabric to pucker if snagged.
The stitching on the Snowbunting is very hard to see.
Quality snaps, zippers, and drawstrings instill confidence in the Feathered Friends Snowbunting.
The fabric on the Snowbunting is sturdier than most, and many of its stitches are hidden.
The Nemo Sonic -20 and Mountain Hardwear Lamina 0 are well-built, with high-quality zippers, sturdy drawstrings, and thoughtful reinforcements. However, while Lamina's exterior fabric is impressively sturdy with few exterior features, Nemo's lightweight, silky exterior is easier to puncture.
The hood design of the Western Mountaineering Kodiak MF. The exterior material is quite delicate.
The drawstrings on the hood and collar of the Kodiak MF are sturdy and easy to use.
The hook and loop tab on the Kodiak MF helps hold its zipper in place, but it is less robust than we'd like.
The Western Mountaineering Kodiak MF bag is well made, but the thin fabric is easier to puncture than the Feathered Friends Bag.
The Marmot Lithium and Never Summer 0 bags fall short in construction quality, with thin, easily punctured fabrics and inconsistent stitching that can snag or bunch. While the zippers are reasonably durable, and the bags have useful features like adjustable hoods and stash pockets, their lightweight fabric and poor-quality stuff sacks are disappointing. Similarly, hood performance proved inconsistent. We found the Lithium built with sturdy and useful drawstrings (both on the hood and at the collar). In comparison, the Never Summer has awkward hood adjustments that detract from its reliability for winter camping.
A look at the exterior and interior material of the Nemo Sonic -20.
A well-designed hood holds in warmth.
The Nemo's reinforced foot box is a nice touch.
A hook-and-loop closure patch holds the neck baffle in place.
The plastic zipper slider protects the fabric from the zipper's teeth on the Nemo Sonic -20.
A large hook and loop closure patch helps hold the collar in place.
Bizarrely, only a few of these bags arrived with a decent stuff sack. Most are made of flimsy fabric and lack compression straps. Only the Nemo Sonic -20, Mountain Hardwear Phantom 0, and Lamina provide a useful stuff sack, though we still prefer to use a high-quality, waterproof compression sack from Sea to Summit.
The Mountain Hardwear Phantom 0 drawstring was a favorite for us.
The fabric is so thin that it's easy to puncture and doesn't hold in as much heat.
The Mountain Hardwear Phantom 0 is well constructed with an easy-to-use drawstring system around the hood.
Weight
A sleeping bag's total weight combines its fill material and shell fabric weight. A bag with higher quality down filling (800 or more) can achieve a lower temperature rating at a lower weight. Meanwhile, high-tech shell fabrics offer weather resistance and durability even in lightweight constructions, like 12-denier shells. Light is right if you're covering long distances, but it usually costs more.
The lightest bag in this review is the Feathered Friends Snowbunting (2.6 lbs), which is especially impressive considering that it's one of the two size-long bags in the test (as opposed to the more common size regular) and features some of the sturdiest fabric. It's super lightweight, and lofty 900+-fill power down makes it all possible, as does its narrow cut.
The Western Mountaineering Kodiak MF only weighs a bit more in size regular at 2.8 lbs (although we think it's important to note the Kodiak MF feels roomier than the Snowbunting due to its 67-inch shoulder girth). In comparison, the Marmot Lithium weighs nearly the same at 2.9 lbs. However, a larger proportion of the Kodiak's weight is in the down fill (1.9 lbs) compared to what is used in the Lithium (1.7 lbs). And the Kodiak's down is higher quality, with an 850-fill power versus the 800-fill power of the Lithium. This combination of fill power and fill weight is why the Kodiak delivers more warmth for its relative weight overall. The Mountain Hardwear Phantom 0 comes in at 3 lbs in a size long, but it's not warm enough to impress.
Purchasing a lightweight bag is an easy way to lighten the load on your next ski tour or winter backpacking trip.
Credit: Jenni Snead
The Nemo Sonic -20 is about a pound heavier than the lightest option tested, in a size regular at 3.7 lbs. It's just as warm as the Kodiak with 2.3 lbs of 800-fill power down, but it's less expensive. We all want a warm, light, and affordable bag, but we usually have to choose two of the three. At 3.8 lbs total, the Marmot Never Summer 0 delivers 2.3 lbs of 650-fill power down, meaning you're not getting as much warmth for the weight you'll carry.
The synthetic Lamina 0 weighs 4.2 lbs, illustrating why people prefer lightweight down over synthetic insulation.
Staying warm and comfy while sitting up, drinking coffee, and even cooking is key in cold winter camping situations.
Credit: Matt Bento
Packed Size
Activities like ski touring can be super gear-intensive. Pack space comes at a premium once you've accounted for a shovel, probe, food, water, layers, and a tent. The same applies to alpine climbing, where your pack may overflow with ropes and cams. Higher-quality down is more compressible than lower-quality options, making it critical in such use cases.
We crammed each bag into our Sea to Summit compression sack and yarded on the compression straps to assess the packed size objectively across the full lineup. Once stuffed and compressed, we measured the resulting dimensions and calculated the relative volume. The results: the good old Western Mountaineering Kodiak MF once again came out on top. It compresses more than all the other bags tested, tucking away into a tidy 12.7 liters. This is why we love the Kodiak so much: a ton of loft and room with a manageable packed size.
The Western Mountaineering Kodiak comes with a low-quality, low-performing stuff sack, yet packs down much more compactly in the standardized compression sack we used for testing (an argument for picking up a better option if you decide this is the bag for you!).
The same is true for the size-long Snowbunting, which packs down to an impressive 16.5 liters.
Some top sleeping bags come with the least useful stuff sacks. We recommend buying replacements if you plan to pack and carry.
The Feathered Friends Snowbunting,Nemo Sonic -20, and Marmot Lithium all pack down to a similar size – 16.5, 16.5, and 16.1 liters, respectively. Keep in mind, though, that the Snowbunting is an extended size long, and the Sonic is rated 20°F below the rest, making their comparable packed size even more impressive.
The Nemo Sonic includes a stuff sack with OK quality compression straps.
The Lithium includes a roll-top sack that does little to improve the bag's packability.
The Nemo Sonic comes with a stuff sack that at least includes compression straps, though they aren't as high quality as we'd like.
The size long Mountain Hardwear Phantom 0 is one of the most compressible bags at 13.9 liters, but it's only suitable for warmer weather, around 20°F or so. The Never Summer is a bit bulkier at 14.5 liters, which is another reason we recommend using it near your car. The synthetic Mountain Hardwear Lamina is unsurprisingly the largest option in the test at 19.3 liters.
Mountain Hardwear offers the best compression straps with the included compression bag.
The Phantom also includes a decent stuff sack, though we still prefer our waterproof Sea to Summit option when packing up for a backcountry adventure.
The Never Summer's drawstring sack is fine for the front country, which is all we would recommend this bag for.
Only the Mountain Hardwear options came with decent compression straps, which is why the less compressible, synthetic Lamina looks smaller than some other bags.
Conclusion
We hope we've unraveled some of the mysteries around selecting the best cold-weather sleeping bag to suit your specific needs. While a good winter sleeping bag may seem like a huge financial investment, it should keep you warm and cozy for years if properly cared for, and nothing beats a good night's sleep under the stars on a long winter's night.
A warm down bag is crucial for a good night of sleep, so that you can feel rested and ready for winter sports action. Here our lead tester is psyched to get up and go skiing.
Credit: Jenni Snead
—Ryan Baker, Matt Bento, Jeff Rogers, Brian Smith, Clark Tate, and Jacob Holmes
