Why do your clothes shrink when you wash them?

The nightmare of your favorite shirt suddenly shrinking after washing is a common one. Why does this happen even when you've followed the instructions? Textile scientists from Swinburne University of Technology have found the answer lies deep within the microstructure of the fabric fibers.

 

1. The "memory" of fabric fibers: The root cause.

Natural fibers like cotton and linen have an irregular and slightly twisted structure. During the manufacturing process, they are stretched, twisted, and straightened to create smooth threads.

1. Hydrogen bonds: These are the chemical "glue" that holds the cellulose molecular chains together.
2. Tension state: After weaving, the fabric is always in a state of forced tension.

 

However, fabric fibers have something called "memory ." When exposed to temperature, humidity, or mechanical stress, they tend to "relax" and return to their original, naturally contracted state.

2. The role of temperature and water

Hot water is the primary factor. It provides the energy to cause the molecules to vibrate violently, breaking the hydrogen bonds.

Element	Impact on fabric fibers
High temperature	Breaking molecular bonds causes the fabric fibers to shrink.
Humidity (Water)	Cellulose is a hydrophilic substance, which causes fabric fibers to swell and become more flexible.
Mechanical impact	The tumbling motion inside the washing machine accelerates the shrinkage process.

Note: Knitted fabrics shrink more easily than woven fabrics due to their loose loop structure, which allows space for the fibers to move.

3. Differences between types of fibers

The shrinkage mechanism is not the same for all types of fabric:

1. Wool: Contains keratin protein with overlapping cuticles. When washed, these cuticles open up and lock together (the phenomenon of felting), making the clothing thicker and smaller.
2. Synthetic fibers (Polyester, Nylon): Have an internal crystalline "framework" that resists twisting and warping, therefore they shrink less than natural fabrics.

4. The secret to saving shrunken clothes using fabric softener.

If you accidentally damage your precious shirt, you can try this scientific trick:

1. Soaking: Mix 1 tablespoon of hair conditioner or baby shampoo into 1 liter of warm water.
2. Mechanism: Fabric softeners contain cationic surfactants that temporarily lubricate and soften fabric fibers.
3. Stretching: Gently pull the fabric back to its original shape while it is still damp.
4. Drying: Allow to air dry on a flat surface.