What you Need to Know about Superwash Wool

Some knitters love it others hate it. Superwash wool is a wool yarn which has been altered so that it will not felt when it is washed in a machine. Wool in its natural state has scales on its surface which can only be seen under a microscope. Felting occurs when these scales catch on one another during washing or with abrasion and moisture. 

I'm of the opinion that Superwash is neither good or bad. It's more important to understand it and then decide on a project by project basis if it makes sense for you to use it.

This description comes from Biotechlearn:

"On the outside of the wool fibre is a protective layer of scales called cuticle cells. They overlap like tiles on a roof. The exposed edges of the cells face away from the root end so there’s more friction when you rub the fibre in one direction than the other. This helps wool expel dirt and gives it the ability to felt. Wool felts when fibres are aligned in opposite directions and they become entangled. The scales have a waxy coating chemically bound to the surface. This stops water penetrating the fibre but allows absorption of water vapour. This makes wool water-repellent and resistant to water-based stains."

The Superwash process prevents the scales from binding in one of two ways. Either the fibre is given an acid bath that dissolves the scales or the yarn is coated with a polymer or resin which smooths over the scales and prevents felting. Labels never identify which method was used however, you might be able to feel the difference as you become more familiar with these yarns as the polymer-coated yarn are often described as feeling  slicker than the acid bath version.

Now for some of the negatives. You should know that high heat during washing or drying can damage a Superwash coating. This could eventually lead to felting which is exactly what you are trying to avoid. I recommend tepid to warm water washing on the gentle cycle using a good wool wash product, a short time in the dryer and to finish with flat drying. I have a dryer rack for my machine and I now use it for all of my Superwash projects. This isn't the one I have but it gives you the idea. It sits in the dryer in a way that allows the tumbler to move while it remains stationary.

https://www.amazon.com/Samsung-DC61-01522A-Drying-Rack-Dryer/dp/B005BQS0BY

Also, it is important to know that because the scales of the yarn cannot bind together, Superwash yarns will stretch a little more than non Superwash yarns. This makes proper swatching even more critical to your end results. I've had knitters tell me about their difficulties with Superwash and the one issue I've been able to identify is that they hand wash instead of machine wash and then don't always take the time to roll the knitting into a towel and squeeze out as much moisture as possible before handling the work. I often need a second towel when I hand instead of machine wash this yarn. Superwash definitely sucks up more water than untreated wool.

The benefits to be considered are that for knits meant to be gifted, it might make more sense to choose an machine washable yarn. I like to include the ball band washing instructions for the recipient. Keep in mind that non-knitters are often afraid of wool because of the shrinking and simply don't want to hand wash clothing. Some assume that wool is itchy and Superwash is less likely to be itchy since the scales have been treated and smoothed out. Another benefit is that Superwash yarns (especially the polymer-coated ones) create a slightly more dense fabric with more drape and a little more shine. Depending on your project or your garment preferences they may create a project which you might be happier with.