"Three filaments" refers to foreign fibers mixed into cotton, including non-cotton fibers and colored fibers, such as chemical fibers, hemp filaments, plastic films, plastic filaments, ropes, cloth pieces, paper pieces, human, dog, mouse, chicken, duck and other animal hair, down and so on. Because the "three filaments" are as light, thin and small as cotton fibers, it is difficult to remove them during spinning, and they are often entangled or attached to the yarn strips, which makes the yarn strips dry unevenly, and the neps and impurities in cotton yarn increase and the strength decreases. When weaving, the broken end rate increases, the fabric quality decreases and the production efficiency decreases; When dyeing, due to different coloring, the dyeing effect is not ideal, which affects the appearance. Therefore, "three silk" seriously affects the quality of yarn and cloth, especially leads to the return of export products, causing huge losses to textile enterprises. At present, the "three silk" can only be removed by hand, and many cotton mills have special personnel to select it, which increases the cost by millions of yuan every year, and the quality is still difficult to guarantee. Therefore, some enterprises would rather spend a lot of foreign exchange to import foreign cotton at a high price than use domestic cotton.