For the weight conscious adventurer, choosing a lightweight bag is a easy way to lower the overall weight of your gear, and some situations, a weather resistant winter bag can eliminate the need for a tent or a bivy sack. For cold weather camping in the front country, the right down bag can keep you warm and comfy, and still be light and packable enough for shorter trips in the backcountry. Read on to find out what features you need from a cold weather bag and check out which bags we recommend in the Best Winter Down Bags article.
The Anatomy of a Down Bag
The bags in our 2017 selection all use continuous baffle construction. The Feathered Friends Snowbunting, the Western Mountaineering Versalite, Western Mountaineering Antelope MF, the Mountain Hardwear Phantom Torch 3 the Rab Ascent 900 and the Kelty Cosmic Down 0 employ traditional horizontal baffles to keep the down distributed throughout the bag. This allows for you to shift more down towards the bottom of the bag so you can still sleep comfortably at warmer temperatures, but also could create cold spots if you're not mindful of the where down is distributed.
The Brooks Range Drift -10 and the Big Agnes Storm King 0 use a vertical baffle design called the Insotech Flow. This design features tiny nets arranged incrementally along each baffle, allowing for airflow and heat distribution, but holds the down in place to eliminate cold spots. The Nemo Sonic and the Marmot Col have a hybrid design of vertical and horizontal baffles, allowing for more airflow in some areas, and keeping the down evenly distributed in key spots.
Most heat loss occurs through the head, therefore, a snug fitting, well insulated hood is essential for a warm night's sleep. When weight is a concern, a head hugging hood like the one on the Feathered Friends Snowbunting is a warm, efficient choice. The wider hood designs on the Mountain Hardwear Torch 3 and the Nemo Sonic are great for folks who are spending many nights in a row in their bags and prefer a variety of sleeping positions. When you are trying on a sleeping bag, cinch the hood all the way up and pay attention to how much of your face is exposed. How does it feel when you turn your head to the side? Do you primarily sleep on your side or your back? If you are primarily a side sleeper, then you'll probably prefer a bag with a deeper, wider hood.
The draft collar is an insulated tube that fits around your neck and hopefully fits snuggly under your chin. All the winter down bags have draft collars to prevent cold air from entering through the hood. The Western Mountaineering Antelope MF and the Feathered Friends Snowbunting have thick, lofty draft collars with their own dedicated cinch cord and closure system. The Mountain Hardwear Phantom Torch uses one round cord for the hood and a flat cord for the collar so you can easily discern them in the dark. The Brooks Range Drift has a simple but effective draft collar that shares a cinch cord with the hood, but typically the best collars have their own, independent cinch cords. The REI Co-Op Magma 10 has a draft "yoke" that only cover the top of the neck. We felt this design was not as effective as a full collar.
A full length draft tube is critical to guard you from cold air and moisture that enter the bag through the zipper. We feel that the most effective draft tubes have ample amounts of insulation and hang down over the zipper, like the draft tubes on the Western Mountaineering bags or the Feathered Friends Snowbunting. The Nemo Sonic and the Marmot Col -20 have two draft tubes, located above and below the zipper. Our testers found that this design is less effective and it causes the zipper to snag more.
Tighter fitting footboxes are more thermally efficient and will keep your feet warmer than wider footbox, but a wider footbox makes room for water bottles and boots. The Kelty Cosmic Down and the Feathered Friends Snowbunting have narrow, toasty footboxes, while the Marmot Col -20, the Nemo Sonic, the REI Co-Op-Magma 10 and the Rab Ascent 900 feature more room. The Marmot Col reinforces the interior of the footbox with a thicker fabric to protect the insulation from moisture on your boots.
The best zippers have some type of stiff strip lining on either side. The Western Mountaineering Antelope MF and the Western Mountaineering Versalite have the best zippers of all the bags we tested. They glided easily zip after zip, and never (not once!) snagged. Snagged zippers can usually be mitigated by carefully holding the draft tube out of the way with one hand, while working the zipper with the other. This isn't convenient if you're trying to get out of your bag quickly in the dark, especially with gloved hands. Regardless, make sure your shell fabric doesn't get stuck in the zipper, as careless tugging could rip a hole in the shell fabric.
Stash pockets are useful for keeping headlamps, batteries and phones warm and easily accessible in the dark. The Mountain Hardwear Phantom Torch 3 and The North Face Inferno -20 have small, conveniently located pockets inside the bag over the left side of the chest. Our testers had difficulty finding the pockets on the Marmot Col and the Nemo Sonic in the dark. Alternatively, some folks find the stash pocket annoying when they're moving around inside the bag, and it is easy to keep your small items warm in a sack shoved in the bottom of the bag. When trying out a bag with a stash pocket, try to access the pocket with your eyes closed, and put your phone or wallet in there to see how it might affect your slumber.
Most winter down bags have shell fabrics with some degree of water resistance. Bags with higher denier fabric and a DWR treatment like the Marmot Col -20 are going to be the most weather resistant, but the lighter shell fabrics on the Brooks Range Drift -10, the Western Mountaineering Versalite, and the Mountain Hardwear Phantom Torch 3 proved to be adequately water resistant enough to withstand frozen precip. If you plan on sleeping exposed without a tent or bivy sack, consider a more weather resistant bag, just know that lightweight weatherproof fabrics are more expensive. If you're carrying a tent, then your bag only needs to be water resistant enough to resist condensation.
Types of Down
Down insulation is made from the tiny, fluffy particles that are found beneath a bird's feathers. The highest quality down comes from geese. Down's quality is measured in fill power, which is the number of cubic inches displaced by 1 ounce of down. The higher the quality of the down insulation, the better the bag's warmth-to-weight ratio will be. 900 fill power is best down available, and the Feathered Friends Snowbunting is the only bag in our 2017 review that has certified 900 fill down. The other top dogs in the review all feature at least 800 fill power down. The Rab Ascent 900 and the Kelty Cosmic 0 use down insulation from ducks. This type of down is generally much less expensive and has a lower fill power. These bags are as warm as some of their high fill power goose down equipped competitors, but are significantly heavier. If weight is less of a concern for your winter camping missions, a bag with duck down can keep you warm and save you a few hundred bucks.
The process of harvesting down is done in many ways. Some methods involve killing the birds (sometimes using the meat, sometimes not), while others take to live-plucking of breast feathers. The eider duck lines its nest with down, whereby harvesting is painless. Live-plucking, which tends to occur on a regular basis, is considered a cruel and painful process by many animal rights activists. Some sleeping bag manufacturers choose to source the down from their products as ethically as possible. For example, Western Mountaineering gets naturally shed down from molting for their products, refusing to accept live-plucked down or down from animals that were force-fed. If this is an issue for you, seek out companies like Western Mountaineering and Patagonia who take ethically sourcing their materials seriously.
Hydrophobic coated down has the potential to radically address down insulation's only drawback- its susceptibility to loft loss from moisture. Nano technology coatings claim to prevent down from absorbing water and allow it to dry out faster once it does absorb water. Hydrophobic coatings have the potential to make a very good thing even better. But how much better and is it worth the additional 10% price increase? The Kelty Cosmic Down 0, the Rab Ascent 900, the Big Agnes Storm King 0, and the Brooks Range Drift -10 all use some form of hydrophobic down. As of now, we haven't developed a way to test whether or not hydrophobic down significantly affects the re-lofting and drying times of the sleeping bags that use it. Currently, the weather resisting properties of shell fabrics are the key, observable factors that affect how much water a bag absorbs, or how fast it dries.
Caring for your Winter Down Bag
The single most important thing you can do to extend the life of your down bag is to store it as fully lofted as possible. Western Mountaineering includes huge storage sacks with their extremely lofty bags. If your bag is even slightly compressed in its storage sack, get a bigger one! For cleaning your bag, use a mild soap designed for cleaning down garments and sleeping bags. Do not use harsh detergents that could affect the DWR treatment on the shell or the relofting properties on the insulation.
Simple precautions like sleeping on a lightweight tarp will help protect your bag from abrasions and puncture wounds. If your bag does have an unfortunate encounter with a sharp rock or stick, or gets caught in a zipper, immediately patch it with whatever is available to prevent down loss. When you get out of the field you can apply a more permanent patch job, and most manufacturers offer repair services at a reasonable price.
EN Testing: Why We Don't Rely On It
The European Norm 13537 is a standardized test created to measure warmth. A copper mannequin dressed in long underwear and socks and equipped with 20 temperature-sensitive sensors lays atop a closed cell sleeping pad inside the bag being tested. The bag is elevated on a 12mm thick wooden platform. Inside a temperature-controlled room, the sensors and algorithmic models calculate the warmth of a given sleeping bag. The results are pared into three categories:
Comfort Limit: based on a standard woman having a comfortable night of sleep.
Lower Limit: the minimum temp that the average person can sleep comfortably.
Extreme Rating: a survival rating for a standard woman.
Note that women generally sleep colder than men. Manufacturers recognize this and most pads and bags are designed to be a little warmer for women.
The EN Rating is just a comparative guide. Like all standardized tests, it often struggles to capture real-world conditions. For example, most of us are back sleepers so the test measure sleeping bag performace for that. But if you're a side sleeper and the bag is better designed to retain heat in a side sleeping position, the test will miss that.
Another factor to consider is the warmth of your sleeping pad. Most pads today are much warmer than the EN sleeping pad used in testing. The pad employed in the EN testing is a thin, closed cell pad. These typically have an R-value of 1. Today's pads are inflatable and relatively lightweight. The Therm-a-Rest NeoAirXLite is more than 300% warmer with an R-value of 3.2, yet only weighs 12 oz. A warmer sleeping pad means the less insulation you need from a sleeping bag.
Several sleeping bags reviewed here have no EN test rating. Having such tests done increases expenses while the value of the data gained from testing is debatable. Furthermore, some bag designs might not be compatible with this standardized test. Quilts and non-traditional models often lack hoods or bottom insulation. The EN rating doesn't account for these designs.
Other real-world factors lead us at OutdoorGearLab to take the EN rating with a large grain of salt. Sleeping positions, clothing worn, type of tent or shelter, and the food and drinks you consume before hitting the hay. Perhaps most importantly, the fit of the bag plays a pivotal roll in warmth. We prefer to rely on our testers' warmth assessments.