How to Calculate Fabric Shrinkage? Why Does Fabric Shrink?

When the fiber absorbs water, it will swell to a certain extent. Usually the fiber swelling is anisotropic (except nylon), that is, the length is shortened and the diameter is increased.

The difference in length between the fabric before and after it is put into water and the percentage of its original length is usually called shrinkage. The stronger the water absorption capacity, the more intense the swelling, the higher the shrinkage, and the worse the dimensional stability of the fabric.

How to calculate fabric shrinkage?

The length of the fabric itself is different from the length of the yarn (silk) thread used, and the difference between the two is usually expressed by the shrinkage rate.

Shrinkage (%) = [yarn (silk) line length - fabric length] / fabric length

Causes of shrinkage

1. When the fibers are being spun, or when the yarns are being woven and dyed, the yarn fibers in the fabric are stretched or deformed by external forces, and internal stress is generated in the yarn fibers and fabric structure. In the static dry relaxation state, or the static wet relaxation state, or in the dynamic wet relaxation state or the full relaxation state, the internal stress is released to varying degrees, so that the yarn fibers and fabric return to their initial state.

2. Different fibers and their fabrics have different shrinkage degrees, which mainly depends on the characteristics of the fibers. Hydrophilic fibers shrink more, such as cotton, linen, viscose and other fibers; while hydrophobic fibers shrink less, such as synthetic fibers.

3. When the fiber is wet, it swells due to the effect of the immersion liquid, making the fiber diameter larger. For example, on the fabric, the fiber curvature radius at the interlacing point of the fabric is forced to increase, resulting in a shortening of the fabric length. For example, cotton fiber swells under the effect of water, the cross-sectional area increases by 40~50%, and the length increases by 1~2%, while synthetic fibers shrink in response to heat, such as boiling water, generally by about 5%.

4. When textile fibers are subjected to heat, their shape and size change and shrink, and they cannot return to their original state after cooling down. This is called fiber thermal shrinkage.