Superwash wool is a special wool product that has been treated or processed in a way that allows it to be machine washable. It's also sometimes referred to as washable wool.
Most knitters who are not allergic or sensitive to wool love using that natural fiber for warmth, springiness, and great wearing in garments. But there are times when conventional wool is not the best choice, such as when making something for a baby that might need to be washed often.
Benefits of Superwash Wool
Many people are afraid to work with wool because it is so easy to shrink. However, some people shrink wool on purpose in a technique commonly called felting—though it's more correctly called fulling. Superwash wool can allow you to work with great fibers without worrying about shrinkage.
Superwash wool is a wonderful choice if you like natural fibers but are giving something as a gift and don't want to burden the recipient with a garment they have to handwash.
It's a great wool choice for babies and kids because parents are busy and you never know when a garment will accidentally get thrown in the washing machine. It just makes life easier not to have to worry as much about losing your work in the wash.
How Superwash Wool Is Made
Superwash wool can be made using an acid bath that removes the "scales" from the fiber, or it can be made by coating the fiber with a polymer that keeps the scales from being able to join together and cause shrinkage.
You probably won't know which method was used on your superwash wool when you buy it in the store, but you might be able to tell when you start knitting. That's because polymer-coated yarn tends to be slicker than regular wool.
Qualities of Superwash Wool
Most of the time it's hard to tell the difference in the knitting between superwash and conventional wool yarn, but author Clara Parkes (the wool whisperer) notes that superwash wools tend to feel a little denser than traditional wool.
These yarns can also be a bit shinier. Sometimes the process used to descale the fiber makes it less able to hold dye, so you should check for colorfastness in your gauge swatch, especially if you're planning to work with more than one color in a project. Superwash merino is the exception, according to Parkes, and it holds dye like a champ.
Another potential problem with superwash wool is that the finished project can stretch quite a lot when you wash it. That's because the scales help provide structure by allowing the yarn to stick to itself. When the scales are gone, there's nothing to hold the fiber to itself. This quality varies widely among different yarns, so as usual, swatching will give you some great information.
Caring for Superwash Wool Garments
To care for superwash wool, wash it on the gentle cycle in your washing machine. A natural-fiber shampoo like you might use for hand-washing non-superwash wools is recommended.
While some superwash wools—particularly fibers intended for use in sock knitting—may say that they're fine to put in the dryer, try to air dry superwash wool projects flat just as you would something washed by hand. You just don't want to take any chances that it might get stretched out or otherwise damaged in the harsh environment of the dryer.