Dimensional Response
Reversible changes in the dimensions of fabrics containing hydrophilic fibers are driven by variations in heat and moisture. This behavior, referred to as thermo-hygral expansion, occurs as the fibers absorb water vapor from the air and swell, causing the yarn crimp to change. It is distinct from permanent shrinkage because the dimensional change can be reversed.
Expansion Mechanism
Swelling of the fiber cross-section increases yarn curvature and forces the fabric to contract or expand depending on the weave structure. Under thermo-hygral expansion, these changes are determined by the elastic properties of the fiber and the yarn twist.
Fabric Stability
Tailored garments can develop puckered seams or wavy surfaces if the outer fabric and lining have different expansion properties. Analyzing the thermo-hygral expansion of each fabric layer ensures that the materials will remain flat under varying humidity. This testing is necessary for high-quality outerwear.
The test evaluates the fabric over a range of relative humidity from thirty to ninety percent. The results are used to predict the appearance of the garment in different climates.
Finishing Control
Textile mills adjust their finishing treatments to minimize the sensitivity of the fabric to moisture changes. The degree of thermo-hygral expansion can be controlled by setting the fabric at specific temperatures and moisture levels. Consistent finishing results in more stable garments for the end user.
This stability is highly valued by apparel brands and consumers alike.
