"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, pieces of paper, 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 wrapped or attached to yarn strips, which makes the yarn evenness uneven, the number of neps and impurities in cotton yarn increases and the strength decreases. When weaving, the broken end rate increases, the quality of cloth surface decreases and the production efficiency decreases; When dyeing, the dyeing effect is not ideal due to different coloring, 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 pick and choose, which increases the cost by millions of yuan every year, and it is still difficult to guarantee the quality. Therefore, some enterprises prefer to spend a lot of foreign exchange to import foreign cotton at a high price rather than use domestic cotton.