Why wool sweaters permanently shrink in hot water

¶ … wash a wool sweater in hot water, it permanently shrinks?

Shrinking of wool sweaters

The world is filled with fascinating little things, which enchant the young and the old alike. There are the fireflies, the falling stars or the multitude of means in which nature provides for mankind. One example in this sense is represented by the sheep, which, along the years, have become emblematic in cultural representations such as stories or even theater plays. And the sheep also have their main function of providing milk; and each year, their wool is cut by the shepherds and turned into valuable pieces of fabric for clothes or coverlets.

Wool is often a preferred material in the creation of soft and warm sweaters, worm by people around the globe to protect them during the colder season. It grows on the skin of most sheep and it has the characteristic of regenerating itself each time after it is cut. The natural wool from sheep is a protein and one of its most notable traits is that it has evolved throughout the millions of years to best attain its objective of protecting the various animals, especially those living in different and difficult climatic conditions. The structure and evolution of the natural wool best distinguish it from the artificial textiles, which have been chemically created by mankind and which serve a specific single function.

"Wool fiber is so resilient and elastic that it can be bent 30,000 times without danger of breaking or damage. Every wool fiber has a natural elasticity and wave or crimp that allows it to be stretched as much as one-third and then spring back into place. Its complex cellular structure also enables it to absorb moisture vapor, but repel liquid. No synthetic fiber has been able to combine all of these characteristics" (Sheep 101, 2012).

Wool is also characterized by the fact that it is easy to dye and flame resistant, and it represents an attractive investment opportunity. Nevertheless, despite these benefits of wool, fact remains that people across the globe have felt frustrated by one specific aspect of their natural wool sweaters -- they permanently shrink when washed in warm water.

The explanation for this phenomenon lays in the very structure of the wool. The material is as such formed from keratin protein, which is covered in microscopic scales. This structure allows for the wool to be flexible and worked with and the microscopic scales allow the textile to capture and retain heat. Still, when washed in warm water, and especially in washing machines during long programs that also include high levels of agitation, the wool sweaters shrink; and when this happens, the process is permanent; on the market, there are some product which claim to reverse the product, but such a process is irreversible.

In essence, when the wool sweaters are subjected to washing in warm water, the microscopic scales lose their space on the fabric and come to cling to one another, as well as the keratin protein. This causes the wool sweaters to shrink and also damages the quality of the fabric, which is no longer able to retain heat.