Down is an ideal insulator for sleeping bags and outerwear—when it’s dry. Get caught in a rainstorm though, and it loses its ability to trap heat. In January, Sierra Designs introduced waterproof down: feathers treated with a hydrophobic nanocoating. In third-party tests, DriDown stayed dry 10 times longer than untreated down, retained 170 percent more loft when wet, and dried 33 percent faster. It also adds almost no extra weight or cost to jackets.