Down is Not Out

In Eastern Mountain Sports in Boston, store manager Dan McDuffie walked me through this year’s winter coats. As we walked past jackets labeled with words like Gore-Tex, Polartec and Primaloft, McDuffie told me that people aren’t buying as much of the artificial stuffing anymore. After Boston’s blizzard in 2015, what people want is a bit old-tech: down feathers.

That’s because despite continued efforts, people have never been able to make a material that insulates better than down. And, unlike synthetic versions, there is almost no manufacturing necessary.

By Fred.leviez - Own work, CC BY-SA 3.0,

By Fred.leviez – Own work, CC BY-SA 3.0,

“When you are buying the fanciest comforter… or you’re buying the most expensive sleeping bag in the world, the feathers inside that sleeping bag, by and large, have gone through absolutely no change,” said Thor Hanson, a biologist and author of Feathers: The Evolution of a Natural Miracle. “All that has happened is that they have been washed and dried. That’s it.”

There are three ways our body loses heat: radiation—which Hanson compares to the heat coming off of a woodstove, conduction (“…if you were to touch the metal surface of that woodstove you

would really get a burn,”) and convection, the heat transferred through a medium, like air. Down feathers are great at slowing or stopping all three.

Down creates a complex lattice of tiny branches known as barbules. Packed together, the barbules weave and interlock, trapping tiny pockets of air that impede radiation. The ends of the barbules are so small and spaced out that heat cannot efficiently be conducted from one to the other. The trapped pockets of air are divided, which slows convention down considerably. So far, no one has been able to create a synthetic material that branches and traps air in the same way that natural down does.

“Down… is just incredible,” said Joe Jackson, Outside Magazine’s Gear Guy. “What (companies) are trying to do is make something that works well outside, and nature has been perfecting that for thousands of years.”

To see this natural engineering, McDuffie led me over to a blue, slim, down jacket. It looked about as insulating as a sheet of paper, but actually it was one of the warmer things you can buy in the


“Not everything has to be puffy,” said McDuffie, folding the entire blue jacket into a ball about the size of my hand.

Only the most expensive feather jackets can take such abuse. According to Hanson, birds have several types of feathers, but real down feathers don’t have a central hard stem, or rachis. Many jackets that seem puffy and warm contain a significant portion of non-down feathers consisting of hard, inflexible rachises The more “true down” you are willing to pay for, the warmer your jacket can be without sacrificing much in bulk.

Fluffy down jacket, from MandleMedia

Fluffy down jacket, By MandleMedia – CC BY-ND 2.0

Despite all the advantages of down, the material has one major weakness: water. “Get a down feather wet… and you’ll see that the barbs stick together more than they do when they are dry,” said Hanson. “As soon as they start sticking together you greatly reduce the amount of air that they are trapping.”

Many manufacturers are creating winter jackets with synthetic alternatives, like PrimaLoft, which is considered to be the next best thing to down. Unlike down, PrimaLoft is made of tiny, polymer microfibers, some of which are as small as 3 microns across—smaller than the width of a red blood cell. These fibers are specifically manufactured to be water resistant, and are additionally sprayed with a water repellent finish. Finally, the fill is crimped like a spring to provide down-like loft and packed into jackets. The trade-offs between insulation and water protection has led many people to flock to synthetic fill. Some companies are developing “treated down,” such as DownTek, to help keep the feathers from getting wet and losing their insulating properties. These technologies have improved down’s reaction to moisture, but it’s not perfect, yet.

Earlier this year, Jackson did a test. He soaked three sleeping bags in water: a synthetic sleeping bag, a down sleeping bag, and a treated down sleeping bag. Then, armed with only his underwear, he took the bags out into the mountain snow, climbed in, and timed how long he could last before the cold got to him. The treated down did well, at 30 minutes, but the synthetic sleeping bag won, at 43.

Although Jackson admits that the test “wasn’t very scientific,” it demonstrated the point: treated down just isn’t there yet. Most people won’t be spending a lot of time this winter in wet sleeping bags in their underwear though.

“Close your eyes and imagine how many times you’ll get soaking wet,” said Jackson, “if the answer is ‘not much,’ go with down.”

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.