Down vs Synthetic Sleeping Bags: Which Insulation Is Better for You?

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If you’re new to the great debate between down vs synthetic sleeping bags, allow me to clue you in. In one corner, we have sleeping bags filled with fluffy down feathers. Their defenders say they are lightweight, space-efficient, and shockingly warm. Their detractors point out that water is down’s kryptonite. Once down gets wet, it’s essentially worthless. In the other corner is synthetic fill, which is championed for its affordability and reliability in all conditions. But synthetic fill is heavier and bulkier than down. 

And then there is the environmental question. Down comes from animals (geese typically, sometimes duck). This can sometimes, though not always, result in animal abuse. But synthetics are basically plastic. And given the growing prevalence of microplastics and forever chemicals in our environment, that doesn’t seem like a great choice, either. 

So which should you choose? To better understand the great debate, I spoke with materials experts Heidi Allen at Nikwax and Tara Maurer at Primaloft. What I learned changed my understanding of the state of sleeping bag insulation and where it’s going in the future.

Table of Contents

Read through the whole article, or tap on a topic below to jump straight to it.

• The Case for Down
• Down and Moisture
• Down Maintenance
• Down Sustainability
• The Case for Synthetic
• Synthetic Thermal Performance
• Synthetic Sustainability
• FAQs
• Final Thoughts

Down vs Synthetic Sleeping Bags: The Case for Down

Let’s start with what down is. Despite the common misconception, down is not the feathers that you see when you look at a goose or duck. Down is the layer of feathers that grow are underneath that waterproof outer layer and sits closest to the animal’s body. If you look at a down feather (keep an eye out for one poking its way through your favorite puffer jacket), you’ll see that it’s made of innumerable wisps connected to a short shaft. 

The lack of structure in these feathers creates a multitude of tiny air pockets, which trap heat from your body and insulate it from the cold outside air. Down-feather quality is measured by fill power (fp), or how much down it takes to fill one cubic inch of space. For instance, one ounce of 550fp down will fill about 9 liters, while one ounce of 900fp will fill almost 15 liters. In sleeping bags, using down with high fill power can result in significant weight savings — an important consideration for backpackers and backpack hunters.  

Down and Moisture

The Achilles heel of down feathers is moisture. When down gets wet, the pockets of air disappear, eliminating virtually all its insulating properties. This is such an issue that Tyler Freel, Outdoor Life’s Alaska-based staff writer, won’t touch it.

“I don’t take down sleeping bags sheep hunting,” Freel said on a recent Outdoor Life podcast. “I’ve had to crawl in my sleeping bag with all my clothes on wet too many times. And my synthetic bag will dry them out overnight.” Freel’s use-case (weeks spent camping and hunting in the unforgiving conditions of backcountry Alaska) might be extreme. Still, there are plenty of people who won’t touch down for exactly these reasons.

Hydrophobic Treatments

In more recent years, sleeping-bag manufacturers have started applying hydrophobic treatments to down feathers to address this issue. I spoke to Heidi Allen at Nikwax to learn more about how this works.

“All hydrophobic down treatments are a water repellent treatment that’s been applied to the actual down feathers,” she tells me. These prevent the down puffs from absorbing water. Nikwax sends its proprietary hydrophobic down treatment (what Allen called “goo”) straight to the company that sources and grades the down. This adds a fairly negligible cost to the final product. Especially when compared to the varying cost of high vs low fill power down. 

Read Next: The Best Sleeping Bags

Nikwax even put its hydrophobic down treatment to the ultimate test. The company floated a person in a sleeping bag on a frigid glacial lake. (The test subject stayed completely dry.) But Allen still isn’t sure she’d recommend Freel take a second look at down sleeping bags given his use-case. “If you’re climbing into your sleeping bag soaking wet, and you’re lying directly on the down, then the weight of your body could cause problems by smashing water into the fill.” 

Down Maintenance

One point that Allen stresses is the importance of maintaining your gear to maximize its performance over time. “If your sleeping bag gets super dirty, even if it’s a hydrophobic down, it’s not going to work as well as it should.” She recommends using a sleeping bag liner. Liners help your sleeping bag’s down maintain its performance. So does regular cleaning. “And then you can actually add a water repellent treatment at home as well,” Allen says. “Nikwax makes a waterproofing treatment for both the outer material and the feathers.”

Whatever you do, just don’t wash your down with a household detergent (more on this below). It’s also important to store down sleeping bags properly. Whatever you do, don’t store your sleeping bag in its stuff sack. Crushing the loft of your down will reduce its insulating properties over time. Yes, it’s usually necessary to pack your sleeping bag in the stuff sack for camping and backcountry travel. When you return from your trip, however, you should air out your bag. Then, store your down bag in a large, loose sack. (Many sleeping bags are sold with these larger storage bags.) Even better, carefully hang your sleeping bag from a hook or hanger for long periods of time.

Read Next: What Is R Value?

Down Sustainability

One issue with water-repellent down treatments is that many of them (although not Nikwax’s) use PFAS. PFAS stands for polyfluoroalkyl substances. There’s been increasing research that shows these cancer-causing chemicals are a detriment to human health and safety. Due to increased awareness and industry pressure (plus new regulations in California), PFAS will likely be phased out of hydrophobic down treatments. However, there may be a drop-off in quality and effectiveness as a result. 

A common misconception about down is that these lightweight, barely-there plumes must be exceedingly fragile. For instance: How many times can you clean them before they fall apart entirely? “Cleaning and re-waterproofing doesn’t actually hurt [down] unless you’re cleaning with a household detergent,” says Allen. “Household detergents are pretty harsh on down feathers and can cause them to get kind of brittle. You get more breakage from those little tiny feathers. So that’s why using a gentle down-specific cleaner is really important for caring for down items.”

In fact, it’s so robust that some of Nikwax’s hydrophobic down is actually made with recycled down from items like bed comforters and pillows.

That’s one issue with down. Another is with how the birds themselves are treated. Nikwax, like many other producers of hydrophobic down, uses only RDS-certified down. RDS stands for “Responsible Down Standard” and it’s focused on animal welfare. The standard ensures that down-producing birds are treated humanely throughout their lifecycle. There is no live plucking of geese in RDS-certified down. (Currently, most down is produced as a byproduct of the food industry.) When shopping for down sleeping bags, look for the RDS certification.

Read Next: The Best Backpacking Sleeping Pads

Our Top Picks for Down Sleeping Bags

If you’re looking to make the switch to down, here are our top recommendations to get you started:

• Best Down Sleeping Bag: Therm-a-Rest Parsec
• Best Budget Down Sleeping Bag: Kelty Galactic

Down vs Synthetic Sleeping Bags: The Case for Synthetic

Down is such a great insulator for sleeping bags that the original synthetic fills were actually designed to mimic it. Primaloft is one of those companies. They were first tasked by the U.S. Army to create a synthetic fill that mimicked the properties of down but didn’t collapse when wet. (Primaloft still supplies the U.S. military with synthetic fill to this day.) Tara Maurer, senior vice president of product strategy, explained that Primaloft’s synthetic insulation excelled at that. Primaloft is made of polyester, which is hydrophobic. The size of the fibers are very small, which means they create surface tension when meshed together. That keeps water at bay.

So, unlike treated down, you never have to worry about the water resistance wearing off. That can be a major help if something goes wrong with your sleep system. “Imagine a scenario where you have a synthetic sleeping bag, and it’s downpouring and it gets wet,” Maurer says. “If you shake it out or wring it out, it will regain its loft and thermal properties faster than down sleeping bags. Particularly untreated down.” And when it does, it will tend to retain that homogenous coverage, rather than clumping together. 

Synthetic Thermal Performance

Speaking with Maurer, it’s clear that that genesis (and instinct for comparison) still looms large over the synthetic market today. For instance, Maurer explained that Primaloft dislikes using fill power as a measurement of synthetic fill, because it’s more of a measurement of volume than it is of thermal performance. The company prefers instead to use a test called the Gustin-Bacon. In this test, a weighted plate is placed on top of 30 grams of fill to see how well the fill resists compression.

Read Next: The Best Sleeping Bags for Camping, Tested and Reviewed

Fluff Doesn’t Necessarily Mean Warmth

But it’s not just the fill power measurement that consumers have come to expect from both down and their synthetic counterparts: it’s also the look. People see a marshmallowy puffer jacket, complete with sewn-in baffling, they think warmth. So some synthetic fill is designed explicitly to mimic that appearance. And that’s true for sleeping bags as well. “We’re constantly trying to achieve a balance,” says Maurer. “We want to make our products as thermally efficient as possible, to use the least amount of material to get the highest net benefit.” 

What that means for consumers is that you can’t eyeball the loft of a synthetic sleeping bag and assume the same rules apply as for a down sleeping bag. Instead, look for established ISO ratings. These ratings are achieved using a dummy and thermometers in a temperature-controlled room. Over time, synthetics may even do a better job at sticking to their ISO temperature ratings than down, since they won’t be as affected by errant moisture. With sleeping bags that use batting (imagine a sheet of synthetic insulation) rather than loose fill, you are further protected from issues with cold spots. You might expect to have cold spots when loose fill settles to one spot or another in the baffling. 

Synthetic Sustainability

One interesting thing I learned from Maurer is how synthetic-insulation companies can minimize their environmental footprint. The majority of Primalofts products are made with 80 percent or more recycled fibers. “The beauty about using polyester is that it can be repurposed and reused again and again,” says Maurer. “We’re taking plastic from recycled bottles. And there’s the potential to take our garment using our insulation and repurpose it into something else when it reaches its end of life.”

Nemo’s new Forte sleeping bag, the first in its new Endless Promise series, is one recent example of this. This sleeping bag can be fully recycled at end of life by following attached directions. 

And when that polyester is finally headed to the landfill, that doesn’t mean it will stay there forever and ever, like we expect to happen with synthetic or plastic-based products.

“Some of our products also have an additive to them that help them biodegrade at an accelerated rate,” Maurer says. In tests, in the amount of time it took for untreated polyester to degrade by 1 percent, the polyester treated with the biodegradable additive had degraded by 94 percent.

Our Top Picks for Synthetic Sleeping Bags

Sold on the reliability and affordability of synthetic sleeping bags? Here are two of our favorites:

• Best Synthetic Sleeping Bag: Nemo Forte
• Best Budget Synthetic Sleeping Bag: Marmot Trestles

FAQs

Final Thoughts

If, like me, it’s been a minute since you considered the state of down versus synthetic sleeping bags, there’s good news and bad news. The first is that many of the seemingly intractable issues with both are being tackled head-on by the industry. Down can be water resistant. Synthetic fill can be less environmentally harmful (and it doesn’t need to be so dang thick). But there are also some pieces of the equation that remain the same. High fill power down is still unmatched by synthetic fill for its warmth to weight ratio. Synthetic fill requires less care to get the same level of performance. It also tends to be quite a bit less expensive. Which of these factors is the most important to you will affect your decision. But both are excellent options that will see you through many nights in the backcountry. 

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Source: https://www.outdoorlife.com/gear/down-vs-synthetic-sleeping-bag/