The Science Behind Water-repellent Down

Will water-repellent down bags make synthetic insulation obsolete?

Hikers love fluffy, lightweight, packable down—when it’s dry. But no one likes wet, wilted down, which loses its power to insulate. That’s just one reason synthetic-fill bags have long had a place in a backpacker’s gear closet (the other is affordable pricing). But a new generation of water-repellent down promises to change the way manufacturers make—and hikers use—sleeping bags.

Two companies, Sierra Designs and Down Decor, have devised ways to coat individual feathers with a molecular-level polymer that creates a hydrophobic finish on each plume. We spent several months testing these new fills (Sierra Designs’ is DriDown and Down Decor’s is DownTek) in a variety of products, and the improvement over untreated down is remarkable. Even in soggy Scotland, the treated down held its loft in conditions that saturated untreated down. Testers detected no difference between the two competitive brands in the field. Backpackers going on long trips will appreciate treated down’s advantages (in bags) the most. It’s rare that a bag gets totally soaked. But on extended trips, especially in cold conditions, body moisture migrates into the down, reducing loft over time.

The treated stuff will hold up much better than standard feathers, and there is virtually no difference in feel, loft, compressibility, or durability. The best part? New-school down doesn’t cost much more (up to $30) than the untreated version. You should still consider synthetic fill if price is a big concern and packability is not. But whether you want a light bag for long treks or for wet conditions (or you just want the peace of mind of knowing your bag won’t wilt in an accidental dunking), you should consider an upgrade.

Bonus: Water-resistant down is also available in puffy jackets, and in this application the advantage is obvious, even to the casual user: There’s no need to pull on a shell in wet flurries—and potentially sweat-soak the down from the inside as you heat up. That’s why we gave Editors’ Choice Snow Awards to the Sierra Designs Tov and the L.L. Bean Ultralight 850.

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