Walk into any outdoor shop and you’re immediately awash in a sea of synthetic materials. Nylon and polyester are everywhere, their virtues—Lightweight! Durable! Fast drying!—extolled in everything from tents to fleece to rain jackets. But when it comes to insulation, one natural material radically outperforms the best synthetic alternatives: goose down. This is its story.
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Ducks and geese produce down to provide insulation from the water, primarily on their chests and underbellies. (They also use it, to a lesser extent, to line nests.) The vast majority of commercial down comes from locations overseas, where ducks and geese are raised for food. “Eighty percent of the world’s down comes from China and younger birds,” says Blake Boyer, client relations manager at the International Down and Feathers Laboratory (IDFL), the nation’s leading test facility for down quality control. “Higher-end down usually comes from Eastern European countries, especially Hungary, Ukraine, and Poland, where geese are raised longer per local taste preferences.”
Plumage is collected when the birds are slaughtered for food. It has three components: feathers, down clusters, and plumules. Feathers are, well, feathers—largely flat, two-dimensional objects. Down clusters, on the other hand, are puffy, spherical, and three-dimensional. Plumules fall somewhere in between, with some degree of irregular three-dimensional structure. On U.S. product labels, a percentage of “down” is listed, which refers to both clusters and plumules.
A single bird produces several ounces of down and feathers. “From one goose you’ll get approximately 300 grams [10 ounces] of feathers and down, or 60 grams [2 ounces] of down,” Boyer says. Down size is related to the age of bird; as a general rule, older animals produce larger clusters. “A single high-end down cluster from an older bird will be larger in diameter than a quarter, or about the size of a large gumball,” he notes.
The clusters provide down’s unparalleled warmth-to-weight ratio. “The key is their three-dimensional shape,” Boyer explains. Down clusters consist of multiple branches radiating from a central point, or quill, where the cluster attaches to the bird. Thousands of tiny fibrils, or barbs, diverge from the branches, each featuring an extensive array of microscopic, hook-like “nodes” along their length. These nodes enable the fibrils to interlock and create an extensive honeycomb of dead air spaces that provides its insulating ability.
What makes down remarkable is how little mass is required to create such an elaborate structure, which is why down compresses so radically and stuffs to such tiny dimensions. Down is also extraordinarily resilient to compression. Composed of the same type of keratin proteins found in hair, down fibers readily bend without breaking and quickly rebound to their original form once decompressed. With proper care and washing, down can retain its original warmth and loft for decades. “Usually the fabric wears out long before the down does,” Boyer says.
The quality of down is measured in terms of its fill power, a number that represents the volume (in cubic inches) of an ounce of goose down under strictly controlled laboratory settings. The higher the fill power, the warmer the down is for its weight. Most commercial down hovers in the 500-600 fill power range; high-quality down features fill powers of 700 and above, due to a higher percentage of large clusters and fewer plumules. The highest commercially available fill power is around 900, close to the theoretical natural limit. “We test over 10,000 samples/year, including Patagonia, Marmot, Mountain Hardwear, REI, Western Mountaineering…all the major outdoor players,” Boyer says. “The highest fill power we’ve ever seen is right around 1,000.”
Synthetic insulations do retain some advantages over down, notably their ability to handle moisture, but even the most advanced are still far from unseating down as the king of insulation. “There’s been a lot of money and research to create a synthetic alternative,” Boyer says. “But that warmth-to-weight ratio is just so hard to capture. They just can’t touch it.”