It's light. It's flexible. It withstands frigid temperatures on top of a mountain. And in the entire history of humans staying warm, nobody's been able to beat it. Here's how you build the most powerfully simple jacket in the world.


Why Are We Still Using Down?

You probably don't think much about down jackets. Maybe you own one. If you don't, a lot of people around you sure do. But why would you contemplate them? They're jackets! They're utilitarian. But they're ubiquitous—and for good reason. Despite centuries of our attempts to create better ways to keep warm, we've never been able to come close to the insulating power of a well-built down jacket. Period. Go ahead, science—throw your best synthetic miracle fabric at down, and watch it shiver.


While it is as perfect as we've seen for warmth to weight ratios, rain gets down, well, down. It's best for dry, cold climates—in other words, treated down doesn't play well with water, unlike when its still attached to a bird. Get wet (or take a bad wipeout in the snow), and your shields may go down—the feathers lose their weather-pounding power completely when soaked.

But down is ultra-compressible.

It's ultra-durable.



And if you take care of it, it'll last decades.

It is, simply, the world's warmest material for its weight. And weight matters. Try climbing thousands of feet up an incline of rock and ice with anything but the lightest on your back. You won't make it far.

But despite down's incredible power as an insulator, you can't just stuff it in there and wipe your feathery hands clean of it. A good jacket—even one built with down—is a well-designed jacket. The reason down jackets go unnoticed—and the reason that, really, they look mostly the same—is that they require an extremely careful balance of factors. Factors that prevent you from walking around looking like you have lumpy, liquidation sale pillows strapped across you.

Down Is More than Your Average Feather

The neatest part of the down jacket's design is that, unlike, say, a CPU, or solar panel, its entire reason for being is obvious just from looking at it. You can study the form of a down garment and—if you know what to look for—realize how and why it was designed to be just the way it looks. It's the perfect example of form following function, an object without any unnecessary parts. When a designer has done their job right, there's nothing left to strip away. Just the down, and the stuff holding it in place. But that's the tricky part, right—so how exactly does it work?


Eric Rice is an industrial designer for Patagonia. He knows exactly how it works—so I spoke with him about the intricacies of that bundle of cloth and goose feathers that stands between you and and agonizing alpine death (or uncomfortable morning commute). He created the down sweater, a legendary garment you probably either own or see around you everywhere—suffice it to say, the man is deft with down.

Before you think about building a jacket with down, you need to know down itself, he told me. Down is, basically, feathers. But screw basically. Eric explained that the magic of down lies in the fact that, when you get up close to it, it possesses incredible microscopic properties.


What you see here in these microscopic illustrations, is a down feather. Really, really close up. Close enough that you'll be able to spot its super powers. Down ain't just a feather—its details are wonderful.


If you zoom in a little, there's a level of main plumes. The kind you'd see branching off of any feather. Zoom further, and there's an entirely new level of secondary plumes branching off from each of the first. Zoom in more (you can do it!), and—that's right—a third layer of even tinier plumes, each one ending in a pointed little bulb. And it's these tiny, tiny bulbs that cast the spell of warmth on ye. One down feather is nothing. Two down feathers are nothing. But a coat full of them creates an incredibly complex structure of bulb-against-bulb, causing microscopic tensions that hold each down feather up, instead of just sagging with gravity.


Think of it as a tiny, feathery skyscraper. The whole thing stands up because of the cooperation of its parts. And this "standing," this downy structure, is what designers (and outdoor buffs) call "loft." Loft is basically a fancy term for fluffiness—but it's the most important term of all when constructing a jacket. The better the loft—the fluffier the down padding—the more air is trapped inside the coat, and the less awful cold seeps in. Strong, fluffy feathers mean strong, winter-pounding jackets. Wearing the right coat, you've got yourself wrapped inside a goose feather thermos.

And again, not a single engineer, scientist, or enemy of the world's goose population has been able to beat this incredible microscopic feather effect. The fluff effect is supreme. But it's also delicate—too delicate for a dousing, as mentioned above. So there've been attempts to beat down—most notably, synthetics like PrimaLoft have hoped to trump the feather with water-resistant properties. But these imitators have never been as warm at the same weight as down, and are often quite expensive to produce. They also rely on chemical manufacturing, like anything else synthetic—compare that to the infinite renewability of a bird. The goose has the last quack.


Building a Shield Against the Cold

So now that you have the right down, you need to know what to do with it. You can't just fill up a jacket like a sack. Down needs to be stabilized, Eric explains, in very particular ways. The design process behind any down coat, jacket, or sweater is determined by a couple of simple questions: how warm do you want it, and how light do you want it? As mentioned, you've probably noticed that most down jackets look pretty much the same: covered in puffy, horizontal down-filled lines. Each line, or "quilt," is bigger, smaller, fatter, or thinner, depending on how you're going to use it.


So how are you going to use it?



If you want something nimble, something light, something to throw on when you go out on a cool day—you'll want a series of thin, dense, ribbon-like strips. Narrower strips? Less down. Less down? Less bulk. Bend down, tie your shoe; reach up, pick an apple. A thin layer for the chilly.

Snow day? Mountaineering? Big. Bigger quilts, but fewer of them. Each larger quilt gives the down more room to loft—more room to fluff out. More mass. More fluff. More insulation. Armor for the cold. A thick shield. A warm body—who cares what's out there whipping against you? You've got an extra hide. Jackets like this—heavy duty down jackets—have more sizable, rectangular padding, not the neat stripes of their dextrous cousins.


But the setup can be adjusted further—because down isn't just down. Like many things in life, it comes in grades. There's wonderful, expensive, fluffiest down of the highest quality. There's total shit down. To tell the difference, a rating system is used to measure a down's "fill power"—that is to say, how much the down lofts. How much it can stretch out and keep you warm. Again, like many things in life, the higher the better. A decent fill power—something 500 or up—means you can do more with less. And less means lighter. If you use better down (which comes from a more mature goose), you use less of it, as it's able to make the aforementioned insulating structure without need for assistance from other feathers. Go all the way up to 800 or 900 fill power down, and you've got a hell of a nice, lightweight jacket—whether you're building it with small pouches or large.

What If You Need It Even WARMER?

So you have your down. You have your cold-smashing, microscopic super-connections. You have your quilts. Now you put it all together. The distinct lines you see across a down jacket are where the quilts are sewn into discrete pockets, sealed off from one another to keep the feathers in place. For most of our purposes, this is fine—and it's the norm. But, Eric pointed out, wherever there's stitching, there's no down—there's no protection at all. Cold can stick an arrow right in there. Nothing between you and the frost but a thin layer of synthetic whatever. Again, no so big a deal on your morning commute, but in alpine conditions, you don't want any Achilles stitching. For situations like this, designers use what's called "baffled" construction—the hardest of hardcore jacket builds.


A baffled coat puts shields under your shields—placing even more insulating pockets within the structure of the garment itself: behind each line of stitching is another down-filled tube that winds all the way around, meaning there's no weak spots for cold to grab a handhold. It's also a hell of a lot pricier.

But How Do You Keep the Feathers Inside?

I needed to ask Eric one more thing. How do you keep the feathers from poking out? That is the worst. And it's the reason the design process doesn't end when you pick out feathers and a way to bundle them together—what you wrap them in seals the deal. A final choice of fabrics is paramount. Here, synthetic materials do come in handy, making strange bedfellows with their all-natural insides. And you have to be picky. A "down-proof" fabric will be windproof, lightweight, and tightly-woven enough to keep those pesky plumes from sticking out and making you look like you just escaped a tar and feathering.


So. Feathers. Quilted pouches to put the feathers in—of the exact shape you need them. Stitched together. Made from just the right cloth. Stick a zipper and a logo on 'er, and you have yourself a jacket. And yet, each second you spend zipping up was preceded by an exhaustive balancing act of warmth, weight, cost, and convenience. Number crunching, loft-measuring, fabric testing—all considered to keep you warm with a material that goes back longer than we've even been wearing clothes in the first place.

David Evison/Shutterstock

You see that thing on your desk? Or that thing outside of your window? It's more than just a thing. Every single object has a story—and some very smart brains—behind it. D Is for Design is Gizmodo's new weekly guided tour of all the things that surround us—the ones we take for granted, but shouldn't. How they got there, why they way they are, and why we should all take a closer look at things, sometimes.