Synthetic fiber made by spinning polyvinyl alcohol as raw material. The polyvinyl formal fiber obtained by treating this fiber with formaldehyde is called vinylon in China and vinylon in the world. Compared with low-molecular-weight polyvinyl alcohol as the raw material, the fiber made by spinning is water-soluble and is called water-soluble polyvinyl alcohol fiber. The general polyvinyl alcohol fiber does not have the necessary hot water resistance and has little practical application value. Polyvinyl formal fiber has the characteristics of softness and warmth, especially the moisture absorption rate (up to 5%) is relatively high among the varieties of synthetic fibers, so it is called synthetic cotton; but its heat resistance is poor, and its softening point is only 120°C.