when you throw a sweater marked "gently hand-washed" into the washing machine and stir it, you may witness an amazing change in size.

so why does the sweater shrink?

the shrinkage of wool fabric is generally called felting. The key factors of this phenomenon are the force and the special structure of wool.

similar to human hair, magnifying the wool surface can also be seen that there is a hair scale structure arranged in one direction. The existence of these hair scales gives animal hair fibers such as wool a special property: when moving in two directions, the friction force is different, the resistance along the hair scale direction is small, and the resistance against the hair scale is relatively large.

(under the electron microscope, the four fabric fibers on the left are all animal hair, and the right is followed by silk, hemp, cotton and chemical fiber)

so, under appropriate conditions, wool becomes somewhat similar to the existence of ribbons. Even if it is repeatedly subjected to forces in different directions, it will only move in one direction, and the more it gets stuck, the tighter it gets. Because the fiber can not be put back with the same amount of reverse force, it will be "stuck" by greater resistance when moving in the opposite direction. As long as the wool fabric is constantly exerted with appropriate force, the fibers can become more and more stuck in one direction and cannot return to the original position by themselves. Felting /shrinkage occurs when the originally loose fabric fibers are tightly entangled with each other and cannot be put back into place.

(like a tie with an one-way buckle, the felt wool becomes tighter and tighter in one direction. Unable to return)

Wool fabric solution environment, temperature, fiber diameter, length, elasticity and so on will affect the felting degree. The heat will make the shrinkage worse. The way you weave can also have an impact, and loose fabrics have more room for shrinkage. In addition, wool can be felted without adding water-just keep poking it with a barbed needle, which we craftsmen call needles.

(this activity is essentially the same as shrinking sweaters)

the most essential prerequisite for felting is a unidirectional hair scale structure, which is unique to animal hair. therefore, felting will not occur in chemical fiber or cotton clothes. There are also some pretreatment methods to reduce the felting properties of wool, such as chemical surface treatment.

of course, if you want to prevent shrinking when washing clothes, you have to think about it from the perspective of environment and force. Follow the "gentle washing" on the washing label and avoid rubbing your sweater as much as possible.

(of course, if you want wool felt, you can do it the other way around: rub it hard with water and soap! (this is wet felt)

PS: after washing and shrinking a sweater, I decided never to buy a sweater again.

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