(1) At the time of spinning, weaving and dyeing of yarns, the yarn fibers in the fabric are elongated or deformed by external forces, and at the same time the yarn fibers and fabric structures are subjected to internal stress, either in static dry relaxation or in static wet relaxation, or in the dynamic wet relaxation state, or fully relaxed state, the release of stress is in different degrees, to restore the yarn fiber and fabric to the initial state.

(2) The degree of shrinkage of different fibers and their fabrics are different, which mainly depend on the characteristics of the fibers-hydrophilic fibers, such as cotton, hemp, viscose, etc. Hydrophobic fibers have less shrinkage, such as synthetic fibers.

(3) When the fiber is wetted, the fiber is expanded under the action of dipping solution, which causes the fiber diameter to become larger. For example, on the fabric, the radius of curvature of the fiber at the interweaving point of the fabric is increased, and the length of the fabric is shortened. For example, the cotton fiber expanded under the action of water, the cross-sectional area increased by 40% and the length increased by 1-2%, while the synthetic fiber was about 5% for heat shrinkage, such as boiling water shrinkage, etc.

(4) When the textile fiber is heated, the shape and size of the fiber change and shrink, and it can not return to the initial state after cooling, which is called the thermal shrinkage of the fiber. The percentage of length before and after thermal shrinkage is called thermal shrinkage, which is generally measured by boiling water shrinkage. In boiling water at 100 ℃, the percentage of fiber length shrinkage is expressed. There are also hot air ways to measure the percentage of shrinkage in hot air over 100 ℃. Fibers also behave differently under different conditions such as internal structure, heating temperature, time, etc. For example, processing polyester, the boiling water shrinkage rate of staple fiber is 1%, the boiling water shrinkage rate of vinylon fiber is 5%, and the shrinkage rate of chlorine fiber hot air is 50%. The fiber is closely related to the textile processing and the dimensional stability of the fabric, which provides some basis for the design of the post-working procedure.