Wool often in the processing of stretching， curling， twisting and other external forces， so that the fiber to change the original form. Wool felt Because wool has good elasticity， it attempts to return to its original form， so in the fiber produced a variety of internal stress， which requires a considerable period of time gradually decay until the elimination， it is often to wool products processing Causing difficulties， which is one of the factors of the size and shape instability of wool products during processing and use. Wool plasticity refers to the wool in hot and humid conditions， can make its internal stress rapidly decay， and can change the existing form of external forces， and then cooled or dried to maintain the nature of the shape.
　　The plasticity of wool is closely related to the change of the conformation of the skin chain and the disassembly and reconstruction of the accessory bond between the two chains. Wool fibers subject to tensile stress are treated in hot water or steam for a short time. And then remove the external force and let it shrink in the steam， the fiber can shrink to shorter than the original length， a phenomenon called “over shrinkage.” The reason for this phenomenon is that the external force and the role of wet and heat skin conformation change， the original deputy bond was broken， but because of the treatment time is very short， not yet in the new position to establish a new secondary bond， Skin chain can be free to shrink， it has produced shrinkage. If the role of the tensile stress of wool fibers in hot water or steam treatment for a long time， remove the external force does not return to the original length of the fiber. However， when treated at higher temperatures， the fibers can still shrink， a phenomenon known as “tentative.” The reason for this phenomenon is that after the sub-key is disassembled， the new sub-key has not been completely established in the new spell and the combination is not stable enough. Therefore， it can only temporarily stabilize the morphology and can still meet the appropriate conditions Retraction. If the elongation of wool fibers in hot water or steam for a longer period of time （such as I a 2h）， then remove the external force， even after steaming， only a slight contraction of fibers， a phenomenon called “Yongding ”. This is because the processing time is longer， the deputy bond is disassembled， in the new position and establish a new， solid secondary bond， the skin chain of the conformation stabilized， which can prevent the wool fiber from the deformation back to its original state， So produce “Yongding.”
　　Wool fabric shape is the use of wool fiber plasticity， the wool fabric in a certain temperature， humidity and external force processing for a certain period of time， through the skin between the deputy bond disassembly and reconstruction， to obtain a stable size and shape. Woolen fabric in the dyeing and finishing process of cooking it， steamed it， the voltage and constant amplitude drying and so has a shaping effect. Whether they are “tentative” or “water-stable” depends on the conditions and effects of shaping， and there is no definite boundary between them.
　　Wool garment ironing is also Lee plastic wool on May， Nirvana， heat and pressure， so that the garment becomes flat without wrinkles， the formation of the fold can also be maintained for a long time.