Pure oil silk and tsumugi silk belong to natural silk, while real silk refers to silk made from silkworm or spider silk. Since tsumugi silk is a blend of mulberry silk, cocoon silk, and wild silk, rather than from a single source, some people may question whether tsumugi silk qualifies as real silk. However, according to the definition by the International Fiber Organization, real silk refers to silk made from the silk of silkworms (such as silver reel silkworms and tussah silkworms) and some wild silkworm species (like the axe-holding silkworm, spicy silkworm, and mulberry hook silkworm), or spider silk (such as from the golden phoenix spider and Emei spider). Therefore, tsumugi silk also falls within the category of real silk.