Underwear is made of blue crystal viscose fiber, because viscose fiber is the scientific name of ordinary rayon, and it is very comfortable to make underwear with rayon, because rayon is actually a purified cellulose fiber with the same molecular structure as cotton.

Cotton grows on the ground, so it is called natural fiber. Artificial cotton is made by re-crushing cottonseed hull and cotton linter bark through a series of technological processes, and then re-spinning. Because it is renewable, it has an impact on the environment, especially the ordinary artificial cotton process has a greater pollution to the environment. The artificial cotton produced by Blue Whale Company has a different process, which is more environmentally friendly than ordinary artificial cotton and has a short process flow, so some people call artificial cotton green fiber.