It is a down-filled futon (down comforter) filled with down feathers of gooses or ducks. The goose has larger down cluster than the duck, so the goose down comforter becomes bulkier. Umo-butons are much lighter than hane-butons and have higher heat-retaining properties. A good-quality umo-buton can be used for several decades by changing its outer and lining fabrics or having it professionally-cleaned.