Under the hot and humid conditions, the fiber aggregates gradually shrink and compact under the repeated action of mechanical external forces, intertwined and felted with each other. This property is called felting property of wool fiber. The processing technology of using this characteristic to treat sweaters is called woolen sweater felting. Shrinkage is a main content in the process of woolen sweater finishing. In order to create good conditions and speed up the shrinkage, chemical reagents are usually added in the shrinkage process. At present, the felting process is mainly used for woolen sweaters such as cashmere, camel hair, rabbit hair, fat wool and Shetland wool, etc. Worsted woolen sweaters are often wet-washed or lightly felted at room temperature for a short time to improve their appearance. I. Purpose of Shrinking The purpose of cashmere shrinking of woolen sweater is mainly to improve and enhance the internal quality and appearance of woolen sweater products. (1) Shrinkage can make the fabric compact, shorten the length, increase the weight and thickness per square meter, and improve the strength, elasticity and warmth retention. ② A layer of fluff is exposed on the surface of felt woolen sweater, which makes it beautiful, rich, soft and soft in color. In addition, the fluff produced by felting plays a role in diluting and covering up some original defects of the sweater, so that it is not obviously exposed on the fabric surface. Second, the mechanism of felting wool sweater can be felted mainly because wool fiber itself has felting performance, which is the internal cause; Certain temperature and humidity conditions, chemical reagents and external forces are the external factors that promote the shrinkage of wool fibers. Cashmere of sweaters has the following internal reasons. 1. Scales of wool The surface of wool fiber is covered with scales, and the free end of scales points to the tip of wool fiber. When there is shrinkage agent, wool fiber wets and expands, and scales open. At this time, when wool is subjected to a certain external force, wool fibers will move. Because the movement of surface scales has directional friction effect, its movement direction must point to the root end. After mourning the external force, the adjacent wool fiber scales are staggered, so that the wool stays in a new position. When it is subjected to external force again, the wool fibers will move relatively, and the external force will be repeated many times, so that the wool will creep slowly, the fibers will be entangled, and the wool heads will protrude from the surface, resulting in the phenomenon of cashmere shrinkage. Therefore, the existence of scales is the most fundamental reason why wool fibers can be felted. That is to say, only fibers with the appearance of scale structure can shrink, and the more scales, the more favorable it is to shrink; However, fibers without scale structure have no contractibility, such as chemical fibers such as acrylic fiber. 2. Wool Curl Because wool fiber has a bilateral structure, the fiber has a natural spatial curl. When the external force makes the wool stretch, the wool will be straightened, and when the external force is removed, the wool will return to the curled state, and the adjacent wool will be entangled in this process. When wool is squeezed, wool fibers will move and creep. This movement has no fixed direction, but it is chaotic and irregular, which makes wool fibers interweave with each other, so the more curly wool is, the easier it is to entangle, and the more favorable it is for wool shrinkage. 3. The elastic wool fiber of wool will deform when it is subjected to external force. Because of the good resilience of wool fibers, when the external force is removed, the sudden elastic deformation will recover quickly, resulting in relative movement between fibers. When external force is applied repeatedly, this kind of relative motion will occur between fibers for many times, which will promote the interweaving and entanglement between fibers and be beneficial to the process of felting. 4. Gelatinization of scale layer In the process of felting, because wool fiber is soaked in hot felting solution, the tip of tile-like scale covering the fiber surface is easy to gelatinize, and under external pressure, local adhesion may occur between fibers at the gelatinized position, which is beneficial to felting. Sweater felting is a complex process, which is the result of interaction and mutual influence of many factors. But the fundamental point lies in the existence of scales, which makes wool fibers intertwine and move directionally under the action of various forces, thus achieving the purpose of shrinkage.