Choosing the Right Bag
We considered over 100 bags and took many painstaking hours to select the ones included in our review; in the end, we picked bags that we liked for different reasons. Our review includes a wide range of 3-season backpacking oriented sleeping bags from incredibly light and compact down bags to some high-performance synthetic bags, to a handful of bags with unique designs that offer exceptional comfort. We've also included a few budget-friendly down sleeping bags and reliable synthetic sleeping bags.
First, carefully consider the most common application of your sleeping bag. Yes, these are all backpacking oriented bags rated from 20-35F, but some models are more versatile regarding where and when you can use them, while others are best suited for specific conditions or trip objectives; some will also offer particular advantages when used under the right circumstances. If on a budget, try to avoid skimping on quality; look for a bag that balances warmth, weight, and versatility. If possible, consider two bags, a lower-priced sleeping bag for car camping/campground camping and a lightweight bag for backpacking and mountaineering.
You don't necessarily need to buy a 20F bag for a future trip that you might go on one day. Instead, buy a bag for the type of trip you most frequently go on. For the occasional colder trip, just plan to wear more layers. This will save you from carrying a bunch of necessary weight over time and it means you wont overheat on a majority of your trips.
To figure out what characteristics you should be prioritizing, you should reflect on what types of trips you enjoy and the types of conditions you are most likely to encounter. Do you frequently backpack in wet conditions on say, coastal hikes? Where a quick-drying synthetic bag is best? Or do you embark on long-distance journeys where weight and pack space are at a premium? Are you someone who simply hates sleeping on their back or wants a little more leg room?
Sleeping bags are one of the most important components of an overnight gear kit. A warm and comfortable bag can make or break a good night's sleep, and a good night's sleep will allow you to perform better on your next day's hike. Sleeping bags are also the most efficient way to keep your body warm; they're much warmer per unit of weight than any type of clothing. Thus, for the weight conscious adventurer, choosing the best bag is arguably the second best way (after a tent) to the reduce weight of a kit. This article describes construction, discusses the numerous types available, and shares some tips and tricks that our testers have learned from testing dozens of products over many years.
To see which products we like the best, see our Best Backpacking Sleeping Bag Review.
The first and arguably most important factor to consider when purchasing a sleeping bag is what type of insulation material is best to keep you warm. Backpacking sleeping bags are available with either down or synthetic insulation. The chosen application of the sleeping bag, the environment and seasons in which you are traveling, your budget, and your experience level will help to determine which insulation material is best for your new sleeping bag. There are several differences but the main three characteristics to focus on when deciding between the two are: synthetic materials ability to insulated when wet and dry much, much faster than down, down's vastly superior weight, compress-ability, longevity (lasting 4-times as long on average) and lastly, cost; with down generally running around twice, or more the cost of a similarly rated synthetic model.
We reviewed far fewer synthetic bags than down bags primarily because other than synthetic insulations ability to maintain loft and thus their warmth is far better than down when wet. The drying time is much faster, and we think for most people, it's worth it to spend a little more money and get a bag that generally speaking performs better and will last 2+ times as long. The old mantra of "Synthetic bags keep you warm, when wet" is mostly true, but it's worth remembering a soaking wet sleeping bag isn't that warm even if its insulated with synthetic materials.
In our side-by-side testing, we found that synthetic bags dried in about 20% of the time as a comparably wet down bag and offered far better, but not perfect insulation when wet. However in the end, because of the trade-off of reduced longevity, almost double the weight, and double the packed size, we chose to review more down bags.
It's also not that difficult to keep your down bag dry in most climates, though there are exceptions; with a waterproof stuff sack or even just a garbage bag, it typically isn't too difficult. Remember a little condensation on your down bag is NOT soaking it and will have virtually no effect on its loft and warmth. Tester Ian Nicholson, who guides in very damp Pacific Northwest over 70 nights a year, exclusively uses down bags. However, if you mostly camp in damper areas or are truly on a budget, then synthetic bags could be the way to go.
Down sleeping bags have a much higher warmth-to-weight ratio, are more compressible, and last 2-4 times longer than their synthetic counterparts. Down bags pack down to roughly a half the size of their synthetic counterparts and weigh on average about 30-50% less. Our review team thinks the biggest reason to buy a down option is that a well cared for bag (AKA not leaving it in a compression sack for months-on-end and drying it out after use) will last most people 20 or more years or even more. On the other hand, synthetic insulation will break down and lose loft over time; most synthetic bags will lose a significant amount (20-30% percent) of their warmth after just five years of average use.
The primary downsides to down bags are that they more expensive and they lose loft when wet; this means a down bag will not keep very you warm if soaked or even partially wet (more than just condensation) and takes roughly fives times as long to dry out. Not all down is created equal; all down used in the outdoor recreation world is assigned a "fill-power", which is a quality rating that affects how much insulation a given weight of down provides. Higher quality (AKA higher fill-power) bags offer more insulation for a given weight; therefore, less weight of down insulation is required to achieve the same loft and subsequent warmth.
Water Resistant Down
Several of the bags we tested, like the REI Co-op Igneo 25, feature hydrophobic down. Hydrophobic down can be created in slightly different proprietary ways, depending on the manufacturer, but the process involves using a molecular-level polymer-coating on the down clusters to develop improved water resistance (which also makes the fibers more hydrophobic).
A report by the International Down and Feather Testing Laboratory noted that on average, hydrophobic down "absorbed 5.2% less weight in water," but "trapped" roughly half the water weight as the untreated sample and dried about 30% quicker.
Some companies have claimed that their treated down insulation "stays dry ten times longer, retains 170% more loft when exposed to moisture, and dries 33% faster than untreated down". Our only problem with those statements is they are they tend to be quite vague; they don't specifically say what those numbers are compared against, nor do they explain how they are getting those drying times.
Our side-by-side testing can't seem to replicate results quite as good as they claim. In our testing, both side-by-side in the "lab" as well as in the real world, we didn't find there was that big of a difference. With light amounts of water in our spray bottle test, treated down did appear to absorb less water and dried roughly 25% faster. In "full soaking-wet tests", there was less of a difference. In real world testing, our testing team noticed even less of a difference and think hydrophobic options didn't practically appear to offer a significant amount of water-resistance, nor were their drying times much faster.
Goose Down Versus Duck Down
According to International Down and Feather Testing Laboratory (IDFL), the world's most significant and one of the foremost authorities on down and feather insulation, geese tend to produce a better product. They offer a more consistent and higher volume of overall higher quality loft and longevity when compared to Duck down; that certainly doesn't mean that all goose down is better than all duck down.
There is quite a range of quality in both types of insulation and high quality duck down is still far superior than mediocre quality goose down. You can find high quality 800+ fill duck down; there is just much less of it compared to goose down. This happens because down clusters from geese are generally bigger than ducks because they typically come from larger, older birds. Because goose down clusters are bigger, they have the ability to produce a larger volume of higher fill-powers on a more regular basis and offer slightly better overall longevity.
There is a big difference in the supply chains of different down manufacturers. No company raises geese or ducks strictly for their feathers; they are bred for meat, which while rarely eaten in the United States, are regularly eaten in eastern Europe and China (and the down feathers are a by-product). Most reputable outdoor brands pride themselves on down that's reasonable sourced, avoiding live plucking and offering the animals a decent living environment.
Shell fabrics and water resistance
We examined each model's shell fabric and its overall performance, comparing each models water resistance, thickness, down proof-ness (where applicable), and comfort against our skin and durability.Denier
Denier (D) is used to determine the thickness of fabric by comparing the number and width of the fibers in a given material. While this impacts the strength of a fabric, it technically refers more to the weight of a specific nylon fabric, though there is some correlation with strength.
While higher denier numbers generally mean greater strength, that isn't always the case. Take for example the Sea to Summit Spark III which uses an extremely low weight 10D fabric, which is both water resistant and down-proof. You could have a lesser quality 15D fabric that would be less down proof and even less strong.
Bags in our review range mostly from 10D with the Sea to Summit Spark III and 12D used in the both of the Western Mountaineering models, to 75D in the case of the Kelty Tuck; most models were around 30-50D.
Why this matters to you; just taking into account the shell fabric, the lightest models we tested are 15 to 20 percent lighter compared with average bags using 30-50D nylon shells.Shell Durability
The lightest bags in our review aren't quite as durable as far as abrasion or puncture resistance as heavier bags, but no sleeping bag that we tested is extremely durable if it's being rubbed up against rocks or comes into contact wit sharp objects. We don't typically find the lower denier bags are a significant disadvantage because sleeping bags don't see that much wear and tear as far as abrasions go. Most things that could cut a hole in a 12D bag would cut a 50D bag just as easily.
The most water resistant bags we tested were the Western Mountaineering UltraLite and the Western Mountaineering MegaLite. All used a very water-resistant shell and solid DWR coating. Our testers were impressed at how these bags minimized the amount of condensation they would absorb. That said, none of these bags were even close to waterproof; if you think there was even a chance your bag was going to get soaked, we would hope you realized that ahead of time and took the necessary precautions (or brought a synthetic bag).
Care of The Sleeping Bag
Proper care is essential for prolonging the life of your sleeping bag regardless of the insulation type and helps maintain their longevity, loft, and warmth. In the short term, keeping down bags dry is imperative for them to function as an insulating layer at all on your trip. However, your down bag will eventually dry out just fine, and it isn't necessarily bad for it to get wet from a long-term longevity standpoint.
See our Best Sleeping Bag Stuff Sacks review for suggestions on in the field storage options. Storing your sleeping bag at home in a large, breathable storage bag where the down or synthetic insulation is not even partially compressed will maintain loft FAR LONGER. Washing down bags with a very mild soap designed (AKA no detergent) for washing down garments and sleeping bags is important. Western mountaineering has a great page found here that is dedicated to the ongoing care of down sleeping bags and garments.
Synthetic sleeping bags take less maintenance in the short term. They can experience more moisture and remain warm and are generally less fragile than their lightweight down counterparts. They are also less stressful to wash, as the insulation tends to not clump when wet and can be dried easily. However, the nature of synthetic insulation fibers leads them to deteriorate more quickly than down. It is imperative to compress these bags as little as possible over time, as the more the fibers get squeezed and then allowed to expand, the faster they lose their insulation qualities. For this reason, a high quality down sleeping bag is a better investment in the long run. Down bags can be compressed over and over and with a few minutes to stretch, the down will return to its lofty self for years to come.
Don't pull the down OUT of your sleeping bag!!!
All down bags will leak some down at some point, regardless of exterior material or craftsmanship. Certainly, higher quality bags will typically leak less down over time, but some leakage is inevitable. When your bag leaks down and there is a plum of down hanging half-hanging-out DON'T pull it out from the outside. This will actually make the hole larger and encourage more down to eventually leak out. Instead, pinch the feather plum from the inside and pull in back into the bag. This will make it less likely that more down will escape in the same spot.
Down can be harvested in a variety of ways. Some birds are killed for their down and meat, while others are killed solely for their down. Some birds, geese, in particular, are live-plucked of their breast feathers. Others, such as the eider duck, line their nests with down, making harvest a pain-free process. Animal rights activists consider live-plucking to be a cruel and painful process, especially because it happens regularly. Some companies, such as Patagonia, do not use down from live-plucked geese or down harvested from animals that were force-fed in order to produce foie gras. Some of the smallest premium companies, such as Western Mountaineering, source the highest down from geese that aren't live-plucked or force-fed; they collect naturally shed down from molting. Some vegans might consider avoiding down products or purchase them from a company such as Western Mountaineering, that guarantee no harm to animals.Down quality has not improved over time.
Fill power ratings have increased over time as fill power testing procedures have changed. Fill power ratings represent the maximum potential performance under ideal laboratory conditions, i.e. after a one-ounce sample of down has gone through a five-day "spa retreat" of washing and drying and fluffing. Geese have not developed better ways to produce down; we've simply improved our ability to test down's potential performance under ideal conditions. The result is that fill ratings today are roughly 130 points higher than they were fifteen years ago, even though the down is the same.
Unlike insulated jackets, sleeping bags are rarely exposed to abrasive conditions that might tear a fabric. Thus, quality backpacking bags use very lightweight fabrics. Some ripstop fabrics, used on the exterior, weigh as little as 0.8 oz per square yard. All of our top-rated bags use very similar, if not the same fabrics. In general, lower-priced bags use heavier fabrics. Lightweight fabrics are very comfortable.
We've found that waterproof/breathable fabrics are unnecessary on a backpacking bag in "three-season" conditions. The exception here is in the bag's foot box. We like how Nemo uses a waterproof/breathable fabric on the bottom of its bags, which helps to prevent the insulation from absorbing condensation from the foot of your tent. In general, waterproof/breathable fabrics are best reserved for winter bags, where there is significantly more condensation inside of a shelter and keeping insulation dry at all costs is a safety concern.
Types of Construction
Three-season down bags use three major types of baffles (compartments for down).
These baffles have a seam that pierces through both fabrics; this is the lightest, coldest, and cheapest way to build a down bag. See the Western Mountaineering Highlite and Mountain Hardwear MTN Speed 32 for examples of this.
These baffles run from the bag's head to toe, and usually, have several mesh walls to prevent the down from migrating. Vertical baffles make it easy to construct comfortable hoods and toe boxes.
These baffles create the highest warmth-to-weight ratio and are used in what we believe to be the best three-season and winter bags. Continuous horizontal baffles offer the greatest versatility for three-season conditions because they allow you to shift down from the top of the bag to the bottom of the bag for warm weather, and from the bottom to the top of the bag for cold weather. Our highest rated backpacking bags have continuous horizontal baffles.
Synthetic bags are constructed in similar ways. Some are sewn-through, others alternate the location of seams to increase warmth.
Types of Sleeping Bags
It has been argued that traditional style bags are overkill for many situations and come with significant pitfalls for the weight and function conscious. But they are indeed very versatile overall. They adapt to different environments well, and are user-friendly. Traditional style bags are a good choice for most backpackers, climbers, and car-campers. Let's discuss some of the pitfalls of the traditional bag for the uber weight conscious and function-oriented users:
Insulation works because it provides open space for warm air to collect close to your body. If it is compressed, there is no dead air space within the insulation material for the warm air. If you sleep on your back, the insulation in the bag is compressed to the point that it does not provide any more insulative quality than your sleeping pad itself. In this case, you may consider the weight of that insulation to be wasted. However, some people move in their sleep and with practice they can move with the bag and keep themselves wrapped in insulation. If you remove insulation from the bottom of the bag, it should have a way to attach to the sleeping pad so that you can move within the bag, and thus not expose the uninsulated bottom of the bag to cold air. A quality sleeping pad is a necessary piece of your sleeping system. They provide insulation from the ground and make for a more comfortable night's sleep.
Zippers provide an easy entry and exit to and from the bag but are heavy. They require extra sewing to attach them to the bag and the zipper itself weighs more than necessary. However, traditional, hooded bags are tough to get into and out of without zippers. One solution for the weight conscious is to consider lightweight bags such as the Sea to Summit Spark Sp III and the Mountain Hardwear Mtn Speed 32, which both use shorter ½-¾ length zippers to save some weight. Look for bags with good draft tubes along the zipper to keep warm air in and cold air out. Keep zippers clean and treat them with care in order to keep from breaking them. We like tape-stiffened draft tubes like those on the Western Mountaineering models which provide for snag-free zipping and unzipping.
Hoods are unnecessary if it is warm out, and they can be uncomfortable. It is true that hoods can create a stuffy and hot sleeping environment during warm nights. The cords, velcro, buttons, and locks that adjust and close hoods can be a nuisance to operate and uncomfortable to lay on. We address these issues when rating the comfort of the products in our reviews. Consider a hoodless bag if you are very weight conscious, sensitive to the closeness of the fit of a hood and if you are confident that the conditions you are using the bag in are suitable for using a detachable hood or hooded clothing to provide the insulation that you need.
Applications for Traditional Bags
The best application for traditional style bags is three-season use. They are good choices for people who need a bag that can go from car-camping to backpacking across a wide range of conditions/temperature ranges. Traditional bags are also a good choice when comfort and warmth are top priority. This may be changing with the introduction of the "Backcountry Bed" style bag from Sierra Designs.
When weight matters, our testers will use a quilt-style bag. Quilts are light and comfortable, but they require more set-up, aren't well suited for people who move a lot in their sleep, and aren't suitable when temperatures get cold.Clothing and Traditional Bag Fit
There's more innovation and variety with down bags, because down is the highest performance insulation, than with synthetic bags. Choosing the right type of fixed girth bag will come down to efficiency versus comfort. The most efficient bags will give your body just enough room to move a little, but not enough to create drafty dead air space. The most efficient sleep system involves clothing. Our testers choose their clothing and traditional bag with the intention of being just warm enough on the coldest night of a trip. And on the coldest night(s) our testers wear all of their clothes, except waterproof materials, inside of a bag.
When it comes to traditional bag comfort, wiggle room is important. The more space to sprawl about, twist and turn, and toss around-- the better! When choosing the most comfortable bag our testers aim to be warm enough on the coldest night with minimal clothing. Unfortunately, wider bags are less efficient at keeping you warm. Your body heats up the air around you, and when you move (in a wide bag) you may open a pocket of dead space (cold, unheated air) and need to start over by heating up a new area. This is the case with larger mummy bags and all rectangular and semi-rectangular bags. Therefore, from a weight and thermal efficient standpoint, the single most important part of selecting a bag is fit. It is up to you to balance comfort and warmth.
Bottomless Traditional Bags
Feathered Friends Vireo is a hoodless and zipperless bag with more fill in the foot area than chest area- it's designed to be worn with a hooded jacket in colder conditions or used in alone warmer weather.
Adjustable girths are the solution to sleeping bags' greatest drawback - fit. A bag that's too large will leave cold, dead air spaces- the bag is less thermally efficient. A bag that's too tight won't be able to loft properly. Variable girths accommodate changes in clothing (in colder conditions we might wear a lightweight down or synthetic jacket). Traditional style bags are plagued by a fixed circumference that is incapable of adapting to the varying conditions typically found by backpackers. The most thermally efficient traditional bag (a trim-fitting bag) will be too slim to accommodate additional clothing in colder conditions and too slim for a broad-shouldered male friend. Quilts better fit a wider range of conditions and body types and are the best type of bag for weight conscious backpacking.
down hood for colder conditions.
Bed Style Bags
The Anatomy of a Sleeping Bag
Down bags have baffles, or channels, that hold down in place. There are three types: continuous baffles (which allow you to move down from the top to bottom of the bag), vertical baffles (which allow you to move down from the head to the foot), and side block baffles (which keep the down in place for maximum heat retention). We believe that continuous baffles are the most versatile and side-block the warmest.
Most bags have a hood that can be drawn around your head in cold weather. Hoods are important because you lose heat through any exposed portion of your body. Your core and lower body are cozily contained in a sea of insulation in the rest of your bag, but your head can be left out in the cold without a good fitting hood. Since hoods vary in comfort, we encourage you to get inside the bag you're considering and fully tighten the hood and neck baffle. Can you still breathe? Can you turn over or change position without suffocating? Does the draw cord feel constricting or uncomfortable? Try out different bags because hood designs vary considerably.
A neck baffle (a.k.a. draft collar) is an insulated tube that prevents heat loss from around your shoulders and neck. While rectangular or ultralight bags may not have draft collars, they remain an essential component of winter bags. Neck baffles should be sufficiently voluminous to fill the void between your neck and shoulders, but not so gigantic that you feel like you're wearing a tire around your neck. Good neck baffles have elasticized drawcords that stretch when you move. The best neck baffles are asymmetrical to conform to your neck, and have differential pull cords (one round and one flat) so that you can feel what part of the bag you're tightening in the dark.
Since your feet take up more room than your shins do, many bags are designed with flared or trapezoidal foot boxes. Some mountaineering bags have extra space to accommodate boot liners or water bottles.
Thoroughly examine a bag's zipper. The zipper's teeth should be large enough to run smoothly without catching on the fabric. Most bags have a reinforced strip along the inside edge to prevent snagging and eventually tearing, the interior fabric. We especially like the tape-stiffened fabric around the zippers on Western Mountaineering models. Also, make sure the fabric and seams have good integrity. Tug at the seams to make sure they don't open up. The bag's overall construction, features, and finish will determine its quality.
Almost all bags have an insulated tube or flap that runs parallel to the zipper in order to reduce heat loss. Cold weather bags may have two heavily filled draft tubes. The tube(s) should be sewn only to the inner liner material, not all the way through, since that creates holes and air leaks. Draft tubes are often sewn to the top zipper so that they hang down when you sleep. Make sure that the tube is sufficiently large to cover the entire zipper area. Those that are too small can interfere with the zipper, so examine the zipper action before you buy.
Some bags have stash pockets. These are more for fashion than function, but perhaps you might use one for a watch alarm. We think internal pockets are better than external pockets because you can access them without opening up your bag and an alarm will be more likely to wake you up. In our experience it is tough to hear an alarm through the insulation…but maybe your hearing is better than ours.
Several of the zero degree down bags we've tested have waterproof/breathable shell materials. These resist frost, spindrift, and snow, and keep the bag much drier on multi-day trips. We only recommend a waterproof shell for camping on snow and ice. For backpacking specific bags, look for lightweight materials that are comfortable to the touch.
Some companies offer a lifetime warranty on material and workmanship. Others don't. Most will repair damaged bags for a reasonable fee.
Stuff and Storage Sacks
Stuff sacks and compression sacks pack your bag down for your time in the mountains or on the water. Storage sacks let the insulation loft when the bag is not in use. Of the 30 plus bags we've reviewed, none of them include the ideal stuff sack or compression sack. Get yourself a small and light compression sack that's durable enough to withstand several hundred compressions. We have written an excellent article on selecting the best stuff sack.
Tips and Tricks
- Wrap the bottom of your bag in your hardshell or rain shell to prevent it from getting wet from condensation absorbed from the tent wall. How: close the jacket's front zipper, tuck the hood and arms inside, and slide the jacket over the foot of the bag. This prevents condensation (on the inner wall of the tent) from getting your bag wet. It's more important with down bags than synthetic, but don't do it if your jacket is wet. Keep the jacket's arms out and open the pit zips slightly if you find that the jacket isn't breathing enough.
- For cold-weather bags, get a long size. This gives you extra space for clothing, boot liners, batteries, water, and electronics.
- Dress well. Wearing excess layers in a trim-fitting bag will compress the insulation, thereby preventing it from lofting to its fullest and keeping you warm. On the contrary, adding layers will take up dead air space if the bag is too roomy.
- Keep your bag dry. Line your stuff sack with an extra thick trash bag, compress the sleeping bag, twist the garbage bag and tuck it into the stuff sack, and compress further. For multi-day trips, we also recommend lining your backpack with an extra thick trash bag and packing everything inside that. This will keep the contents of your pack dry even during large river crossings where the bottom of your backpack gets submerged.
EN Testing: Why We Don't Rely On It
The European Norm 13537 is a standardized test that measures sleeping bag warmth. The test uses a copper mannequin, fitted with 20 sensors, that wears long underwear and socks, and lies on top of a thin sleeping pad and an elevated 12mm thick wood platform. The mannequin lies inside of a sleeping bag in a temperature-controlled room while its sensors and mathematical models attempt to estimate the bag's warmth. Results from EN testing provide us with three numbers:Comfort Limit: based on a standard woman having a comfortable night's sleep
Lower Limit: the lowest temperature a standard man can sleep comfortably
Extreme Rating: a survival rating for a standard woman
The problem with standardized tests of all types is that they only measure how well a person or product does on the test, and the trial may have little to no correlation to how well that person or a product performs in real-world conditions. Thus, EN testing only measures how well a sleeping bag performs on the EN test. Is EN testing similar to real-world situations? Yes and no.
Most people sleep on their backs, the position the mannequin is in, but not everyone has the same body type as the mannequin, and the EN sleeping pad is no where near as warm as those used by most people today. For example, thin closed cell pads like the one used in EN testing, generally have an R-value around 1. Modern lightweight inflatable pads like the Therm-a-Rest NeoAir XLite (R-value 3.2) are 300%+ warmer. The warmer a pad is, the less insulation you need beneath you, and the less insulation, the lighter the bag. Therefore, bags with little or no insulation on the bottom have poor EN scores. Yet some of us want the lightest gear possible…
Many of OutdoorGear-Lab's highest-rated bags are not EN tested. This is because: 1) they're made by small companies that can't afford the expensive test (Marmot, for example, ships bags to a lab in Norway for testing) 2) some companies may not believe EN testing provides their customers with valuable information, and 3) a bag's design may not be compatible with the test. For example, quilts and all non-traditional bags might not have hoods or insulation on the bottom. Furthermore, factors like an individual's body type, clothing, sleeping pad warmth, type of shelter, and food and drink can all affect one's sleeping experience. And, above all, how a bag fits your body has more influence on warmth than any other bag-specific attribute. We do not believe EN testing is the ultimate method to compare bag warmth across a wide range of bag types. Instead, we rely on our testers' assessment of warmth. Most of our backpacking gear testers have spent so much time playing and sleeping outdoors (years) that they know exactly how their body performs in various conditions and how those conditions will influence how warm they are at night. For example, after v hours of w type of exercise with x to eat and drink, y clothing, and z weather, our testers can assess a sleeping bag's warmth and compare it to previous experiences with other bags after just a few nights. For our purposes, we believe this method is better at comparing a variety of sleeping bags types than EN testing and maybe putting college kids in the meat freezer.
Though this standardized rating does allow for some comparison of warmth across brands, our advice is to approach sleeping bag temperature ratings with some degree of caution. Without significant personal experience with a particular brand or type of sleeping bag, or without significant experience with sleeping bags in general, you should be conservative. Ask questions, read our reviews and get into several sleeping bags to assess their fit and characteristics that contribute to keeping you warm. Continue to eat well and stay hydrated in the outdoors and experiment with different shelters and clothing options for the given conditions. Comparison between bags and your personal systems in a wide range of conditions is a better measurement than any standard. Hopefully you will travel in and experience a wide range of conditions in all of your adventures. We can't all have a bag that is ideal in them all, so aim for something that will be good in most of those situations.