Goose down is the soft, fluffy layer of feathers found beneath the tougher outer feathers of geese. It is known for its excellent insulation properties, making it a popular choice for filling items like 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 how much space an ounce of down occupies. Higher fill power means better insulation and warmth. Goose down is favored over other types of down, such as duck down, for its superior warmth-to-weight ratio and softness.