First a couple answers on the why of superwash wool. Why do people want it?
A big reason is washability. Non-superwash baby gifts can end up doll clothes, and socks that have been tossed accidentally in the washer and dryer barely fit a big toe. Dyers and knitters also love the intense color produced by dyeing on superwash. Lots of folks also say that superwash yarns are softer; they are certainly smoother.
Only a very small percentage of the superwash produced in the United States goes to the hobby market (that’s us knitters).
Much of the US-made superwash wool goes to ready-to-wear fashion, and to the military for uniforms. Wool for military wear is praised for its durability, its suitability in a variety of climates, and its fire resistance. The superwash process makes it washable, and it makes the United States wool pool (a variety of sheep breeds mixed into one yarn) soft enough to wear. The military uses a lot of wool and helps keep wool farming viable in the United States.
What Exactly Is Superwash?
Superwash is a process that makes wool less susceptible to felting when it is washed and dried by machine. There are two ways most commonly used to make a superwash yarn. One is to strip or dull the scales of a fiber, then fill the irregularities left behind with a polymer to smooth the fiber. The other is to coat the fiber to suppress the scales. There are many scientists working on developing new ways of shrink-proofing wool. Most methods are the super secret, proprietary information of the companies and labs developing them.
Felting: It’s All About Scales
Each individual wool fiber is covered with tiny scales, like a snake’s skin. When these little suckers are agitated, literally, that’s how felting happens.
Felting needs moisture, friction, and sometimes a change in temperature like accidentally putting things in the dryer. Wool relaxes in water, even more if it’s warm or hot: the scales open like the hatch on the back of a car. Agitation makes the fibers scootch closer together so that the scales hang on to each other. As the fiber dries the scales slam shut, locking out the ability for fibers to move past each other and locking in the new shrunken size. Your beautiful knitwear is now smaller, stiffer, and not so soft. If you’ve ever knit and then felted a bag or slippers on purpose, you know exactly how much the felting experience can change knitting.
Superwash and the Environment
There are environmental issues with many superwash processes, but not all superwash or anti-felting processes are the same. Different companies use different processes and chemicals, and different countries have different environmental regulations for their wool industry. The only way to know what process your favorite yarn company uses is to ask them.
While many yarn companies don’t know the process their suppliers use, some do, and a growing number are making it a priority to be aware and to choose supplies with the environment in mind. This is true about yarns processed in North America and the rest of the world.
For example, in most countries there are strict regulations on the cleanliness of water that gets dumped from anyindustry, and there are companies that go beyond what the law requires to remove chemicals from their wastewater.
One of the most used methods to make a fiber superwash is to remove or reduce the scales on the fiber with chlorine, either as a gas or as a solution. Then the modified fibers are smoothed with a coat of a polymer.
Chlorine gas is the most toxic way to make superwash, both for the people working in the plants and the environment. A chlorine solution in water is less toxic to workers, and chlorine in this form can be filtered from wastewater.
The polymers used to smooth the fiber are made from different types of plastics. The type most commonly usedis also used in paper processing. It’s a polymer that keeps paper from reverting to pulp when it gets wet.
Newer, more environmentally friendly methods of creating superwash are being developed and used in several different countries. I’ve read about some scientists experimenting with heat, and others working on a coating that biodegrades quickly, making the shrink resistance temporary. All of this work is industrial and secret.
One environmentally friendly method is used by O-Wool. They use a natural (and proprietary) polymer to coat the fiber to keep scales from interlocking. They do not remove or reduce scales, but only smooth them down—like using pomade on unruly hair.
With a regular and a shrink-proofed merino side by side, you get a visual to help connect all the words.