General wool sweater would shrink and be distorted severely after washed in a household washing machine, or even become completely unusable. Now, some brand put forward the "machine washable" wool sweater, indicating it can be washed in household washing machines without shrinkage or deformation. It solves some trouble to manually sweater washing. Why the normally wool sweater can be machine washed? There are two types, one is to blend the wool fibers with other chemical fiber (such as adding acrylic, polyester, etc.) in order to reduce the wool felting. Another is to treat wool sweater a resin-type shrink resistance, so that it can withstand washing in household washing machines. But no matter it is what kind of "machine washable" wool sweaters it is cannot compare with any other clothes that machine washable. Generally the best choice is gentle washing, to prevent unnecessary damage.
Generally, machine washable wool is specially treated wool. Chlorine oxidation is the one commonly used method in which wool fiber is simply immersed in a saturated chlorine chemical reagents and then the chloride react with the outer layer scale, so that scales are partially or wholly softened or strip , therefore reducing performance fulling milling of wool, also resisting shrinkage. The principle is to reduce friction between the fibers to resist shrinkage.