Superwash -- superwashing -- is treating wool chemically so that it can be machine washed without fear of shrinkage, like a towel, etc.
BUT ... there are problems with superwashing that, depending upon the type of superwash and the intended use of the fiber, can outweigh the advantages. We use superwashed warp (lengthwise) fiber/yarn in our Fabric, but not the type of superwash that inhibits the handling of moisture. We use superwashed fiber in our knitted products (Watch Cap and Neck Gaiter, plus the cuffs of our Hooded Jacket), which are normally worn directly on the skin.
Wool is scaly, kind of like a snake. And those scales enable wool to absorb and then adsorb water vapor but repel liquid water, which is key to WeatherWool's All-Weather performance. But the downside to wool's "scaliness" is that the scales can ratchet against each other when agitated ... and the ratcheting effect only goes one way. So the yarns can shrink when agitated, and obviously shrinkage is a problem. (The scales also lend strength to wool yarn because the scales prevent fibers aligned in opposite directions from sliding across each other.)
Superwashing eliminates the ratcheting in one of two ways. One general method of superwashing involves the use of acid baths to eat away at the scales ... no scales, no shrinkage due to ratcheting. Another superwashing method involves coating the wool fibers with a synthetic polymer so that the scales are sort of filled in and smoothed over, and again, the ratcheting is eliminated.
Below left is a photo of an untreated, natural wool fiber. The scales of the fiber are sharply defined. Below right is a photo of a fiber superwashed in hydrochloric acid, showing how the scales have been etched away. At bottom is a fiber superwashed with polymer. The polymer coats the entire fiber and the scales are smoothed over somewhat.
We do not know where these photos came from. We owe someone a PLEASE AND THANK YOU, at the very least. If anyone knows who we can contact, we'd love to hear from you, please. Kathrin from Germany has seen these same photos used by Woolmark, and suggests they own the rights. This would make sense, and THANKS! to Kathryn for pointing us to Woolmark.
There are many variations within the two main methods of superwashing, but the goal is to enable wool garments to be cleaned in a standard wash machine, without shrinking, by eliminating the tendency of the scales to ratchet.
BUT ... Of course there are disadvantages to superwashing, else it would always be done:
- Wool doesn't have those scales for no reason. The spaces between the scales enable water vapor to infiltrate a wool fiber, and enable the fiber to exclude liquid water ... So vapor coming off the body, and humidity from outside air can be slowly taken into the fiber, but the water from rain or even a swim does not enter the fiber. Covering the fibers with polymer reduces or eliminates this behavior. Etching the scales away with acid (the superwash method used on our fiber) also changes the way the wool handles water.
- Covering or eliminating the scales weakens the yarn because scales prevent yarn from stretching and breaking ... when fibers are lined up in opposite directions, the scales prevent the fibers from slipping past each other ... the scales hold the yarn together. Some knitters describe yarns superwashed with polymer as slippery, and they are well-known to stretch over time
- Some people find the feel of polymer-superwashed fiber to be uncomfortable ... much more like a synthetic fiber ... which makes sense, given the synthetic coating on the wool
- Superwashing involves chemical treatments that many would prefer to avoid
- Superwashed wool loses the "memory" ... a woolen garment over time will conform to the wearer, but superwashed wool does not have the garment memory
- Superwashed fiber is more prone to pilling
These differences in properties between superwashed and natural wool fiber make them better or worse for different uses.
WeatherWool completely avoids the use of superwashing for our woven garments. We want great strength and durability and we very much desire the fiber to handle water according to Nature's design. Also, our tops (shirts, jackets) are almost always worn over a base layer, although in unusual circumstances they can certainly be worn comfortably on the skin, and I have personally done so many times. Our Pants are normally worn without a base layer, but Pants don't hug the body, and legs don't generate moisture and oils like the torso.
As mentioned above, however, our two knitted products, the Watch Cap and Neck Gaiter, are worn directly on the head and neck, and washing easily is more desirable. In addition, these are knitted products and the way they are worn and used does not require toughness or strength.
As we grow and gain more experience, we think it likely we will make more knitted products, and as we work more with knits we be looking to eliminate superwashed fiber. We won't use superwashed fiber for the weft (the heart) of our wovens, and we are looking to move away from superwash for our warp as well.
Lastly and importantly, the information presented here is the best I can figure out after doing some research. I'd be more than happy to hear from people who can make it better!!
THANK YOU --- Ralph
13 April 2022 --- Ralph