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. The fibers obtained by spinning relatively low molecular weight polyvinyl alcohol as raw materials are water-soluble and are called water-soluble polyvinyl alcohol fibers. General polyvinyl alcohol fibers do not have the necessary hot water resistance, and have 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.