Goose down is the soft, fluffy layer of feathers found beneath the outer feathers of geese. It is highly valued for its excellent insulation properties, making it a popular filling for comforters, jackets, and sleeping bags. Goose down is lightweight and compressible, providing warmth without adding bulk. The quality of goose down is often measured by its fill power, which indicates its ability to trap air and provide insulation. Higher fill power means better warmth and lighter weight. Goose down is considered superior to other types of down, such as duck down, due to its larger clusters and better thermal efficiency.