ダウン (Feathers) refers to the soft, fluffy feathers found beneath the tougher exterior feathers of birds. These feathers provide insulation, helping to keep birds warm in cold weather. They are commonly used in products like jackets, comforters, and sleeping bags due to their lightweight and excellent thermal properties. The most popular source of down is from geese and ducks. Down is often categorized by its fill power, which measures its loft and insulating ability. Higher fill power indicates better insulation with less weight, making down a preferred choice for outdoor gear and bedding.