Dimensional Change
Size reduction in woven or knitted fabrics after wetting and drying arises from the relaxation of internal stresses locked into the yarns during fabrication. This behavior is structural shrinkage, and it results from the rearrangement of the yarn structure as the fibers swell and de-swell. It differs from fiber shrinkage, which is the thermal contraction of the polymer chains themselves.
Fiber Relaxation
Mechanical stresses applied during spinning, weaving, and knitting stretch the yarns out of their natural, relaxed shapes. When the fabric is immersed in water, the fibers absorb moisture, swell, and release these built-up tensions. This swelling allows the yarns to return to their curved, stable configurations, causing the overall fabric dimensions to contract.
Washing Effect
Domestic laundering accelerates the relaxation process through a combination of wetting, temperature, and mechanical agitation in the washing machine. This agitation helps the yarns overcome the friction holding them in their stretched state. For a cotton jersey fabric, the majority of this contraction occurs during the first few wash cycles, after which the dimensions of the fabric stabilize.
Adding synthetic fibers to a blend can reduce this effect because synthetic polymers absorb less water and swell less than natural cellulose.
Garment Specification
Apparel makers test the wash shrinkage of fabric rolls before cutting to adjust the pattern dimensions accordingly. If the shrinkage is not accounted for, the finished garments will be too small after the first home wash. The factory uses these laboratory results to calculate the necessary size adjustments for each production lot.
