The L size has been changed to the S size again! Why do woolen sweaters always shrink?

A warm wool sweater

It is a must-have item in winter, but many people have this trouble: every time the wool sweater is washed, either the sleeves become shorter or the hem becomes shorter. The original L-size clothes are shrunk to S size, and some are even directly shrunk to children's version. What's going on?

First, let's understand the characteristics of wool. Wool is a natural protein fiber. A single wool fiber consists of a scale layer, a cortex layer, and a medulla layer. The scale layer is the surface layer of wool, which grows in a certain direction. The bottom is connected to the cortex layer, and the other end points to the tip of the hair.

Schematic diagram of the structure of wool fibers at different levels (Source: Textile Materials Science, Editor-in-Chief: Yu Weidong)

Because of this characteristic, the friction they experience in bidirectional motion is different. Moving in the direction of the hair scales has less resistance, while moving in the opposite direction has greater resistance. This phenomenon is called the " directional friction effect ." It is like touching our hair from the root to the end, which is very smooth, but in the opposite direction it feels very rough. The scale layer of wool is richer than that of human hair.

This "directional friction effect" is the key to wool shrinkage . During the washing process, the wool sweater is swung back and forth in the rotating turbine wall of the washing machine. Each filament of the clothing will come into contact with other fibers and produce friction. The scale structure on these fibers is similar to a tiny ratchet device, which can only allow the fibers to slide in a single direction.

The moisture in the washing machine exacerbates this process, causing the fibers to swell and soften the wool scales, which then become entangled with the scales of other wool fibers, forming a knot-like state. During the entire washing and drying process, the tens of thousands of tiny thorn-like structures on the surface of the wool sweater cause the fibers to be more tightly combined, ultimately resulting in a reduction in the overall size of the garment, which is also known as the wool shrinkage .

Therefore, any wool-containing product, especially pure wool products, will shrink to a certain extent after washing, and the shrinkage ratio is usually between 8% and 10%. Moreover, the higher the proportion of wool, the more significant the shrinkage phenomenon. On the contrary, wool products that do not shrink or shrink very little generally have a low wool content.

How to wash a wool sweater?

According to my country's current textile industry standard for wool knitwear FZ/T 73018-2012 "Wool Knitwear", wool products have been divided into three types: dry cleaning, careful hand washing, and machine washing.

If your sweater is "hand wash carefully", you can refer to the following methods when washing:

1. The water temperature for washing clothes should not exceed 30℃. Do not use hot water. The water level should only be enough to cover the clothes.

2. Pour about 20 ml of detergent into a normal-sized wool sweater, stir it evenly with your hands, and soak it for a while.

3. Use a pressing method to clean, and remember not to rub repeatedly. You can gently rub the collar and cuffs that are easy to get dirty.

4. After rinsing, remember not to wring it. Wrap it with a clean towel and squeeze out the water.

5. After washing the sweater, do not hang it on a clothes hanger, otherwise it will deform. The sweater should be squeezed dry, shaken loose and flattened. When drying, it can be placed in a clothes drying basket and then placed in a cool place to dry, but not exposed to the sun.

After drying, the wool sweater can be folded and put into a sealed plastic bag, and placed in a dry wardrobe with moth-proofing agent. Avoid hanging to prevent deformation. For the less visible pilling, you can gently pull it out with your fingers or cut it off with small scissors, and brush it with a clothes brush.

Can a shrunk wool sweater be restored to its original shape?

First, the wool can be treated with hot water or steam to expand it, thereby loosening the interconnections between the scales. This step also softens the fiber and its scales.

Then, by applying external force to stretch, the entanglement between the scales can be effectively untied.

At the same time, during the stretching process, an iron is used to keep the clothes moist and at a suitable high temperature, which can maintain the softness of the scales and further enhance the recovery effect.

The above methods help to remove entanglements and felting between wool fibers.