Along with your shelter and your pack, your quilt or sleeping bag is one of the “big three” items in your kit that can make or break your backpacking trip. While there are important external factors to consider — quilt vs. sleeping bag, draft tubes and zippers vs. minimalism, color, weight, cut, and more —  maybe nothing matters quite like what’s inside your sleep system. 

Down vs. synthetic is a debate that’s been raging for decades now. Luckily, there’s no right or wrong answer. Like so much in ultralight backpacking, it’s a case-dependent question that depends entirely on where you are, what you’re doing, and what you need out of your sleep system. 

In this short guide, we’ll deliver some basics on how and why insulation works, then dive into the great debate. By the end, you’ll feel confident making a choice that works for you. 

 

Enlightened Equipment's Revelation Quilt with APEX synthetic insulation

Insulation 101

What keeps you warm at night? You do. Yes, luckily if you’re reading this, we feel safe in saying there’s a very high chance you’re a mammal, which means you bring your own heating system around with you wherever you go (weight penalty = zilch). 

Insulation works by trapping the body heat your body generates out of noodles and peanut butter. More specifically, insulation traps air, and your body heat warms that air. The better insulation is at trapping air, the warmer you’ll be. 

Loft

That’s why loft is so important. Loft is a term that can be loosely generalized as “how fluffy something is.” 

Consider a cat. In its natural state, which is to say not soaking wet, a cat’s fur has air between all the strands of its fur. Its fur is lofty. Some cats are loftier than others — think Persian vs. American shorthair. 

Now give either of those cats a bath (a human bath, not a cat bath) and watch as the loft collapses. The introduction of moisture has collapsed the empty space between the fur, and now you have two cold, angry cats. The fur will have to dry before it becomes lofty again, and we could reasonably expect the Persian’s fur to take longer to dry and re-loft than the American shorthair’s. 

Types of Insulation 

Now let’s apply this surprisingly cat-centric lesson to the two types of insulations commonly found in backpacking sleep systems: down and synthetic. 

Down

Down feather (Photo: Wikimedia Commons)

 

Down is a type of specialized feather found on most birds, but is especially plentiful on birds who spend a lot of their time in cold and wet environments, like water birds. Down is not interchangeable with the tough outer feathers that protect it — in other words, the feathers in a feather pillow and the down inside your quilt are not the same thing. 

Down is very lofty and traps a lot of air, making it an excellent insulator. Down’s loft is measured in fill-power, a measurement of how much volume a given weight of down occupies. Higher-quality down has a higher fill power, meaning it takes up more space for the same weight as lower-quality down. The outdoor industry uses down with fill-power numbers ranging from 600 to 1000. 

Synthetic Fibers 

 

Synthetic insulation works on the same principle as down — its purpose is to create pockets of trapped air that body heat can warm. The difference springs from its origins. Synthetic insulation is a tangle of petroleum-based fibers, usually polyester, created with the express purpose of mimicking down’s natural properties. 

Yes, it took an industrial revolution and two hundred years of science to do what ducks more or less nailed over 40,000 years ago. 

In any case, the difference in materials and origins means down and synthetic insulation contains different properties, performance considerations, upsides, and downsides.

 

One of Enlightened Equipment's down quilts out in the wild

Down Vs. Synthetic: Pros and Cons

Performance in Moisture 

If you’ve ever pulled a wet bag of down over your shivering body on day five of a six-day backpacking trip, you’ve already discovered down’s major downside — it just doesn’t hold up that well to long-term moisture. 

Using waterproof stuff sacks combined with a waterproof pack and/or a pack liner helps tremendously, but moisture will still get into your down quilt. It’s inevitable, and it comes from two places: condensation dripping off the interior of your shelter and moisture from your body permeating your bag’s face fabric. Over time, this moisture will begin to degrade the insulative properties of your down as the water begins to collapse the loft. 

Synthetic fibers are much less prone to collapse in this manner. Don’t get me wrong — synthetic insulation will collapse if exposed to enough moisture. An absolutely soaking wet synthetic quilt will insulate you just as poorly as an absolutely soaking wet down quilt. But for maintaining warmth on humid trips where condensation and incidental moisture are likely, synthetic is the way to go. 

Some ultralight backpackers on winter or shoulder-season trips have adopted a “best of both worlds” approach. Rather than pack a single down bag with a 0-degree temperature rating, they will opt for a lighter, more packable 20, 30, or 40-degree down quilt, and pair it with a 40 or 50-degree synthetic quilt on top. This technique migrates the dew point to the outside of the synthetic quilt while retaining the loft and warmth of the down quilt. 

Warmth-to-Weight

That all being said, down is still king when it comes to a host of other performance factors. The most noteworthy is warmth-to-weight. If you are an absolute gram counter and know you’ll have moments on your hike to sit your down quilt out in the sun from time to time, you should absolutely choose a down bag. 

As an example, Enlightened Equipment’s (EE) regular/regular 950-FP 20-degree Revelation Sleeping Quilt weighs 20.9 ounces. Meanwhile, the same quilt at the same temperature rating and insulated with APEX synthetic fibers weighs 30.1 ounces. That’s nothing to sneeze at. 

Compression & Packability

A similar product comparison produces a similar win for down in the compression department. 

Keeping the same product specs from the above comparison, we find that EE’s down Revelation compresses to 7 liters, while the synthetic Revelation compresses to 12.5 liters. 

As ultralight packs get smaller and smaller, a 5.5-liter difference is significant and should be taken into account. 

 

El Coyote's AlphaLite 900 down quilts 

Durability, Longevity, Care 

Another place where down shines is in longevity. Down can withstand repeated compressions better than synthetic fibers, which tend to break down after hundreds of instances of stuffing and unstuffing.

Don’t get the impression that a synthetic bag will conk out with occasional use. But if you are putting in over a hundred nights a year in the backcountry — such as you might while thru-hiking — and doing that year after year, it’s something to note. 

This is also a good moment to remind you not to store your quilt in a stuff sack, be it down or synthetic. Make use of the cotton storage sack almost every quilt and sleeping bag manufacturer provides. 

With some ultralight quilts that utilize particularly thin face fabrics, plumules of down might occasionally poke through the fabric. This doesn’t happen with synthetic insulation because it’s typically matted into tight clumps that don’t lend themselves to escape very easily. But this isn’t a point against down — the amount of plumules that escape from your quilt in the course of regular use is insignificant from a warmth standpoint. 

When it comes to caring for your quilt, synthetic holds an edge — slightly. With both types of insulation, you should use a front-loading washer and avoid using standard laundry detergent at all costs. You can buy down or synthetic-specific detergent and such products are equally easy to find online. 

The only difference springs from washing machine settings. Most sources agree that down bags should be washed exclusively on “delicate,” while synthetic bags can stand up to the slightly more rigorous “gentle” cycle. 

 

Ethical Concerns

Because down is by and large a byproduct of the Asian meat industry, and not very many Asians are eating penguins (to my knowledge), the down inside your quilt once belonged to either a duck or a goose. 

It’s important to note that it’s virtually impossible to find down quilts in America that have been sourced by live-plucking birds. It’s simply not a thing to worry about anymore. You can read more about industry initiatives like the Responsible Down Standard here. 

However, some users may have issues with utilizing animal products of any kind, even if those products originated from an animal slaughtered for a different purpose. If that’s you, you’ll want a synthetic option.

On the flip side, the outdoor industry as a whole is wrestling with its dependence on the non-renewable resources used in many of its performance-oriented products. Just as some backpackers may balk at the use of animal products as an insulator, others may want to avoid using synthetic bags for conservation reasons. 

In this department, we’ll leave the decision up to you.

 

Final Thoughts

Is down better than synthetic? If you only ever talk to thru-hikers on the Pacific Crest Trail (or other low-humidity adventuring locales), you might get an unequivocal yes. But it’s a wide, wide, world, and the Mountain West only represents a tiny fraction of the places to participate in the sport of ultralight backpacking. 

There are plenty of backpacking trips where a synthetic quilt will serve you equally well, and some where it’s clearly the best choice. Budget allowing, it’s best to have one of each and choose accordingly. 

If that isn’t a possibility, consider your primary use cases: the temperature, humidity levels, and duration of the trips you are most likely to take, as well as the overall weight and volume of your kit. What type of shelter you use is also a factor, as single-wall shelters tend to suffer from more condensation issues than double-wall shelters. 

Whatever you choose, it’s worth reiterating — given enough moisture, any type of insulation will eventually fail. So do whatever you can to keep your quilt dry, and get it out in the sunshine for a drying session whenever you can while backpacking, especially on longer trips. 

Dyneema Composite Fiber stuff sacks, anyone? 

 

Andrew Marshall has written for Blue Ridge Outdoors, BikeRumor! ExplorersWeb, The Inertia, GearJunkie, Backpacking Light, and other web and print outlets. A committed dilettante with a tendency to be interested in just about everything, Andrew is also a published poet, a chess player (trail name: "Pawn"), a long-distance backpacker, a mountain biker/bikepacker with a tendency to fly over the handlebars, and an extremely slow trail runner. Based in Western North Carolina, he enjoys hanging out with his two-year-old, eating biscuits and gravy, and checking out way more library books than one person could possibly read in three weeks. You can find more of Andrew's writing and watercolor illustrations here.