When a favourite shirt or dress shrinks in the wash, the result can be frustrating, especially if care instructions were followed. Textile scientists explain that some fabrics are more prone to shrinkage than others, and the reasons lie deep within the fibres themselves.
Common plant-based fibres such as cotton and linen are naturally irregular and crinkled. At the microscopic level, they are made of long chains of cellulose molecules that exist in coiled shapes. During manufacturing, these fibres are stretched, twisted and aligned to form smooth threads. Chemical links called hydrogen bonds help hold the chains together, giving strength and cohesion to the fabric. Once woven or knitted, the fibres are locked in place under tension.
However, fibres have what experts call “memory.” When exposed to heat, moisture or mechanical action, they tend to relax and return to their original crinkled state. This explains why some fabrics wrinkle easily and why shrinkage occurs after laundering.
Hot water plays a key role. It increases the energy of fibres, causing them to vibrate and break hydrogen bonds. Loosely knitted fabrics are more vulnerable because their open loops allow greater movement, while tightly woven fabrics resist shrinkage by restricting fibre mobility. Cellulose is also hydrophilic, meaning it attracts water. As water molecules penetrate the fibres, they swell and become more flexible. Combined with the tumbling motion of a washing machine, fibres recoil to their natural state, leading to shrinkage.
Shrinkage is not limited to hot water. As many households have experienced with rayon, cold water can also cause fibres to swell. The effect is less severe, but mechanical agitation still contributes. To reduce the risk, experts recommend cold water, low spin speeds and gentle cycles. Labels may not fully explain the impact of agitation, so choosing a “delicate” setting is often safest.
Different fibres shrink in different ways. Wool, an animal-derived fibre made of keratin proteins, has a surface covered in overlapping scales called cuticle cells. During washing, these scales open and interlock, causing entanglement or “felting.” The result is denser, smaller clothing. Synthetic fibres such as polyester and nylon behave differently. Made from petroleum-based polymers, they contain crystalline regions that act as an internal skeleton, preventing crinkling and making them more resistant to shrinkage.
Researchers are exploring new materials to address the issue. Blended yarns that combine natural and synthetic fibres are one approach. Another involves shape-memory polymers that can change or return to a previous shape when exposed to heat or water. These differ from elastic fibres used in stretch fabrics, which simply bounce back after being stretched.
For garments that have already shrunk, a simple rescue method may help. Soaking the item in lukewarm water mixed with hair conditioner or baby shampoo—about one tablespoon per litre—can temporarily soften fibres. Stretching the fabric gently back into shape and drying it flat or under light tension may restore some size. As scientists explain, “conditioners have chemicals known as cationic surfactants. These will temporarily lubricate the fibres, making them more flexible and allowing you to gently pull everything back into place.” While not a complete reversal, this technique can make clothes wearable again.
Source: Swinburne University of Technology
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