Why Does Fabric Shrink?

Why Does Fabric Shrink?

The phenomenon of shrinkage in textiles refers to the change in length or width that occurs when a fabric undergoes processes such as washing, spinning dry, and drying. The extent of shrinkage varies depending on factors like the type of fiber, the fabric's structure, and the external forces it encounters during manufacturing. Different fibers and fabrics exhibit different levels of shrinkage.

Synthetic fibers and blended textiles generally have the least shrinkage, followed by woolen and linen fabrics with moderate shrinkage. Silk fabrics tend to shrink more significantly, while viscose fibers, artificial cotton, and synthetic fur-like materials experience the highest shrinkage rates. It's worth noting that even though 100% cotton fabrics typically undergo some degree of shrinkage and color fading, the key lies in post-processing treatments. Hence, most household textile fabrics are pre-shrunk. However, it is important to mention that pre-shrinking does not mean the fabric will not shrink at all; rather, it ensures that the shrinkage rate is controlled within the national standard of 3%-4%. Therefore, when purchasing hotel linens, one should consider not only the quality, color, and pattern of the fabric but also its shrinkage rate.

1.Reasons for Fabric Shrinkage

1.During spinning or weaving, yarn fibers can be stretched or deformed due to external forces. When in a static dry or wet relaxed state, or under dynamic wet relaxation conditions, or even in a fully relaxed state, the release of varying degrees of internal stress causes the yarn fibers and fabric to revert to their original form.

2.Different fibers and fabrics exhibit different levels of shrinkage based mainly on the characteristics of the fiber—fibers with high hygroscopicity, such as cotton, hemp, and viscose, tend to shrink more significantly, while hydrophobic fibers like synthetic fibers shrink less.

3.In a moistened state, fibers may swell due to liquid penetration, causing an increase in diameter. In a fabric, this swelling can force an increase in the curvature radius of fibers at the weave points, resulting in a shorter fabric length. For instance, cotton fibers expand in water, increasing their cross-sectional area by 40-50% and length by 1-2%, whereas synthetic fibers tend to shrink under heat, such as boiling water shrinkage, usually around 5%.

4.Textile fibers undergo dimensional changes and shrinkage under heated conditions, which cannot be restored to their initial state upon cooling. This is known as thermal shrinkage, and the percentage change before and after thermal shrinkage is referred to as the thermal shrinkage rate, commonly measured using boiling water tests where the percentage shrinkage at 100°C is recorded. Other methods include using hot air over 100°C or steam above 100°C. Different fibers exhibit varying behavior under differing internal structures and heating conditions; for example, polyester short fibers have a boiling water shrinkage rate of 1%, while viscose has a rate of 5%, and chlorofiber shrinks by 50% under hot air.

2.Factors Affecting Fabric Shrinkage

1.Different raw materials lead to varying shrinkage rates. Generally, fibers with high absorbency tend to swell when wet, resulting in increased diameter and shortened length, thus having higher shrinkage rates. Synthetic fibers, with low absorbency, have lower shrinkage rates.

2.Yarn (thread) construction, influenced by the fiber type and properties such as twist level and tightness, affects the size change in water. Typically, fabrics with thicker yarn have higher shrinkage rates, while those with finer yarn have lower shrinkage rates.

3.The density of the fabric plays a role in determining the shrinkage rate. Fabrics with similar warp and weft densities tend to have similar warp and weft shrinkage rates. Higher warp density results in greater warp shrinkage, and vice versa for higher weft density. Overall, fabrics with higher density tend to have better dimensional stability.

4.The production process of the fabric impacts shrinkage. Fabrics that are subjected to multiple stretching and long processing times with high tension during weaving and finishing generally have higher shrinkage rates. To manage fabric width during actual production, a pre-shrinking process is often employed (as mentioned earlier).

5.Laundry care, including washing, drying, and ironing, influences fabric shrinkage. Hand-washing tends to produce better dimensional stability compared to machine washing, and washing temperature also affects stability – higher temperatures typically result in poorer stability. Proper ironing, using an appropriate temperature according to the fabric composition, can improve the fabric’s shrinkage issue. For instance, cotton and linen fabrics can benefit from high-temperature ironing to reduce shrinkage, but excessive heat can damage synthetic fibers, causing them to become stiff or brittle.

Standard Fabric Shrinkage Rates:

The formal term for "shrinkage rate" is "water wash dimension change rate," which represents the percentage reduction in the dimensions of a textile after washing or immersion in water.

Shrinkage Rate = [(Pre-Wash Dimension - Post-Wash Dimension) / Pre-Wash Dimension] × 100%

Typical rates are:

Cotton: 4% - 10%

Mercerized plain weave cotton: Warp 3.5%, Weft 3.5%

Twill weave cotton: 4%

Mercerized twill weave cotton: Warp 4%, Weft 3%

Plain weave unmercerized cotton: Warp 6%, Weft 2.5%

Polyester: 3.5% - 5.5%

Chemical fibers: 4% - 8%

The magnitude of the fabric's shrinkage rate is an essential criterion for evaluating product quality. It directly impacts later stages of production like grading, pattern-making, cutting, and sewing, as well as influencing production costs and manufacturing complexity, making it a vital standard in assessing the quality of apparel (and home textiles).

This information is from China Hotel Textiles Website.