What’s the deal with superwash?

So you’re making a sweater. You love wool, and you also love saving time, so you probably want to choose the machine washable option – or do you? 

Then again maybe you’ve heard that superwash wool is basically coated with plastic, and you really don’t like plastics, so you want to avoid it at all costs. But is that right?

Really, it’s all a bit more complicated. There are things to love about both options (and honestly, nothing to hate). Let’s break it down. 

What does superwash treatment actually involve?

Animal wool, just like human hair, has scales running along the follicle. These tiny scales are responsible for a lot of wool’s natural behaviour: its bounciness, for example, but also for its tendency to shrink and felt in the washing machine. Since few people are excited to see a “handwash only” instruction, yarn manufacturers have worked hard to find ways to manage these scales and fight shrinkage. 

The most common “superwash” treatment is the chlorine-Hercosett process: first, a chlorinated solution is used to erode the scales themselves, and then a polymer resin (Hercosett 125) is applied to smooth out the surface. 

That means there are three areas of environmental concern: potential pollution from the chlorine, heavy water usage, and the polymer. However, that “plastic coating” is by far the least worrying part. It’s the same stuff as is used in household products such as teabags and paper towels; it’s not toxic, and yarn accounts for a very small proportion of global Hercosett usage. Careful research has also found that superwash wool does not shed microplastics – and it actually biodegrades faster than untreated wool.

The overall impact of superwash treatment probably depends most on where the yarn is made, because responsible production facilities take proper care of their wastewater (and well-regulated countries ensure that). Our suppliers can all demonstrate strong commitment to environmental protections. All in all, the environmental impact of most superwash wool is likely to be a negligible portion of your overall household consumption; and there is no toxic impact.

How does it affect the yarn?

Changing the structure of the wool fibres obviously will have an effect on the yarn’s nature – that’s the whole point! So how will you experience that difference? 

Reducing the scales means reducing wool’s natural buffer: it becomes a little denser. It may lose a little warmth and water resistance, though probably not enough to matter in most situations. Smoothing out the surface makes it a little glossier and, well, smoother! If you’re sensitive to animal fibres, superwash may feel less prickly to you. Superwash also loses some of wool’s natural elasticity, so instead of shrinking, you have to watch out for stretching. And losing the grip that might cause felting also means you lose the toothiness that works so well to hold stitches together in colourwork. On the other hand, you gain an almost silky quality: besides being a bit smoother and glossier, superwash creates a more drapey fabric.

One last distinction: superwash is loved by hand dyers for good reason: superwash takes dye brilliantly, especially when it comes to clever techniques like speckles. Natural wool just doesn’t give the same results.

Here’s a quick compare-and-contrast of their relative advantages: 

But what about washability? Isn’t that a really important factor?

Honestly? Maybe not, or at least not the way you think. I respect the need for easy laundry, I really do! But superwash needs care too. All your knits should be treated with care, because a handknitted fabric just isn’t as sturdy and resilient as factory fabrics (or not in the same way). Rough treatment in the machine might not shrink your garment but it could distort its shape – especially given superwash wool’s tendency to stretch out. And remember, wool actually doesn’t need to be washed very often at all; it is naturally resistant to bacteria and odours. Spot cleaning and regular airing will get you far. (Take a look at this video from Knitting for Olive for insight into how well their merino copes with rough everyday toddler wear!)

For many years now, all my knits have been washed exactly the same way: in the machine, on the wool “handwash” setting, at no higher than 20 degrees C. This isn’t foolproof. It depends on your machine; I know friends whose machines have let them down badly. 

Ultimately, the “best” yarn is always the yarn that fits best to your particular project. If you’re knitting for other people’s kids, for instance (so you’re not doing the laundry), superwash is probably the safest bet! Then again, if you want a traditional Fair Isle cardigan, untreated wool is your best friend. They are just two different options, with different benefits. Enjoy exploring the possibilities.

Further reading:
Clara Parkes, the Knitter’s Book of Yarn
Jillian Moreno, “Superwash part 2: How do they do that?” on Modern Daily Knitting
Anne Vally, “The truth about superwash yarn” on Knit Together (with carefully cited sources!)