Superwash Wool: What you need to know to make the choice
Each individual hair on a sheep has small scales that can open and close in response to heat and moisture. Before these hairs have been sheared off, the scales help regulate the sheep’s body temperature and repel moisture away from the sheep’s skin. They serve the same function after the hairs have been sheared off the sheep and turned into yarn. The scales make wool “breathe,” which helps to regulate temperature and repel moisture away from the skin underneath.
These scales are responsible for the “scratchy” feeling of natural wool. The finer the wool, the smaller the scales, which means the finer the wool the softer it is to the touch. If you think you’re allergic to wool, you’re probably not, since wool is one of the most hypoallergenic materials we make clothes from. But some folks have fine textured skin that is more sensitive to even microscopic irritants…like wool scales.
These scales are also what make wool felt. The scales open up in the presence of moisture and heat. Agitating hot, wet wool tangles these scales together. This in turn pulls the hairs more closely together…which, in turn, tangles the scales more tightly together…which, in turn…you get the idea. The hairs get so tightly drawn together that the overall area will shrink 25-30% in both directions, while, at the same time, it gets thicker and denser. Then when the heat and moisture are gone, the scales close a bit and become bonded together forever, or near enough. Thus, felt.
Some of us do this on purpose to make felt. We knit or crochet or weave wool larger than we think we want it, then subject it to moisture, heat and agitation in order to shrink and thicken it. But we’ve all also had the experience of throwing something into the washer and dryer accidentally and ruining a beloved wooly object.
If only someone would invent a way to make wool impervious to the felting process. If only we could neutralize those pesky scales that make felting possible. If only… But wait! There is such an invention. It’s called The Superwash Process.
How many of you are old enough to remember the permanent waves of the 1940’s, or the 1960’s, or the 1980’s? They stripped away the top layer of each hair and chemically weakened the hair so it could be made flat instead of round. Thus, curls. The superwash process is similar. Manufacturers take raw wool and soak it in a vat of a chlorine based solution. (If you want to know more about the chemistry, you can look at the sites listed in the foot notes below.) This solution chemically burns off the tiny, delicate edges of the scales, leaving them even tinier and very blunt. After rinsing off the chlorine solution, they then soak the wool in a vat of polymer resin. Polymer resin is a generic category and includes chemical compounds such as nylon, and is similar to the resins added to the “wax” they put on your car at the car wash. It means plastic, and it slicks down what remains of the burned off scales so they can’t tangle with their fellows. Thus, superwash.
The result is a wool that can withstand exposure to heat, moisture and agitation without shrinking or felting. Superwash wool is also silkier to the touch, as there are no more protruding scales to prickle against skin. The smoother surface appears more lustrous than untreated wool. It also results in a wool that does not “breathe” the same way untreated wool does. Without those scales, superwash wool doesn’t regulate temperature or repel moisture the way untreated wool does. It also doesn’t last forever.
As I said above, a polymer resin is a kind of plastic, and will melt and deteriorate when exposed to heat. That means every time you toss your superwash wooly objects in the dryer, you are shortening the life of the resin coasting. Polymer resins will also get worn away with friction over time. This will either leave the stumps of the scales poking out, or pull the scales completely off, leaving a roughened surface on the core of the hairs. Your superwash wooly objects will have a longer, prettier shelf life if you treat them delicately. Wash them on gentle cycle in cool water, and don’t put them in the dryer.
Superwash wool seem like a great alternative to unprocessed wool. But remember that it has its own vulnerabilities and requires its own kind of special care. There are folks who have concerns about how the plastics, including polyamide, in our clothing may be affecting our health. So you may want to think about that as well and weigh convenience, durability and comfort when shopping for yarn for your next project.
Chemical composition of superwash process: