All About Superwash Yarn

Journal

Nov 17

Written By Harriet

Lots of the yarn that is commercially available is superwash yarn. This is especially true of sock yarn, which very often contains superwash merino. Here I want to look at what superwash actually is, how it’s different to non-superwash yarn and also talk a bit about our decision not to stock superwash yarn.

How does wool become superwash?

Natural wool fibres consist of a scaly outer layer which repels water, and an inner core which absorbs it. This construction is what enables wool to absorb around 30% of its weight in water without feeling wet, and means that it can ‘wick’ moisture away from the body. It’s what allows sheep to stand out in the rain without getting soaked through. However, when wool fibres are placed in warm water these scales lift up, and if they are cooled quickly or subjected to agitation they cling to each other and cause the fibres to interlock. This is what makes wool shrink and felt, and is the reason that you can’t put your untreated wool jumper in the washing machine.

Superwash wool is fibre that has been treated with a process to prevent shrinking and felting, meaning that it can be machine washed.

Traditionally, most superwash wool has been treated using the Chlorine-Hercosett process, first patented in the US in 1960. With Chlorine-Hercosett, the wool is subjected to a chlorine treatment, which removes the surface of the cuticles that cause felting. It is then rinsed, treated with sulphite and sodium carbonate to reduce the chlorine level and the acidity, and coated in a polymer resin called Hercosett 125 which increases its tensile strength, elongation and abrasion resistance. Finally drying and polymerisation stabilise Hercosett 125, making the wool safe to use.

There are a number of environmental issues with this process. One is the use of chlorine, which can be incredibly unsafe, especially if used in gas form. The process also uses a huge amount of water, which then needs to be cleaned to make it safe again. The UK and US both have strict laws controlling effluent in waste water, but this is not always the case in other parts of the world. Because use of the Chlorine-Hercosett process is restricted in many developed countries, wool is often sent abroad to be superwash treated, increasing its carbon footprint. Finally, the resin used to coat the fibres is a form of plastic. It will eventually break down as the wool is repeatedly washed, releasing micro plastics. Until it has completely broken down, the wool is not biodegradable.

The good news is that there are other, more environmentally friendly processes to make wool machine washable. They usually involve coating the fibres with a plastic or polymer resin that ‘glues’ the scales down, rather than using chlorine to remove them completely. Unfortunately it is quite difficult to find out much information about these processes, either because manufacturers understandably don’t want to share the details in a competitive marketplace, or because the information that is available is very technical. One example of a more environmentally friendly alternative to the traditional superwash process is the EXP process from the Schoeller Spinning group, which uses natural salts instead of chlorine.

What are the benefits of superwash yarn?

It is important to note here that all wool is washable, it’s just that some garments will require more care or a different washing process to others. That said, the biggest advantage of superwash yarn is that it can be easily washed in a machine. This could be really important if you are knitting clothes for children, for example, or gifts for non-knitters, or those who may not have the time to wash their knitted items by hand, for whatever reason.

There are a number of other advantages to superwash yarn. One is that it tends to feel softer in the hand than non superwash yarn - it can even look a little shiny. That’s because the polymer coating has smoothed all the fibres. People who can’t wear untreated wool because it irritates their skin may find garments made from superwash yarn are better for them for this reason.

Superwash yarn also takes dye really well. It no longer has those water resistant scales, so it absorbs water better, allowing dye to penetrate the fibre more easily. It can also be subjected to higher heat and more agitation during the dyeing process without the risk of it felting. Dyers can produce far more intense shades on superwash yarn that they could on untreated yarn.

And the drawbacks?

The fabric produced from superwash yarn can look and feel quite different to non-superwash fabric. It’s not all bad, it just depends on what you are trying to achieve. Superwash fabrics generally have much more drape, and less snapback. The fibres don’t cling on to each other, so garments will need to be washed more often to retain their shape and they may have a tendency to grow or stretch over time. This won’t be a problem with shawls or blankets, but if knitting clothes you will probably want to consider the construction carefully. Sweaters and cardigans with seams have more structure than those without, so work better in superwash yarns that those that are knit in the round. If you use a superwash yarn for a pattern that was designed for a non-superwash yarn, it’s worth noting that you may get quite a different result to what the designer intended.

Because superwash yarn is smoother and more slippery than untreated yarn, it can be more difficult to knit with, and harder to pick up dropped stitches. Bamboo or wooden needles are a good choice for superwash yarn as they are more grippy than metal needles.

Superwash can be great for plain knitting, but it lacks some of the character of untreated wool when it comes to texture and colourwork. The stitches don’t want to grip onto each other, so cables can end up looking a little flat, and superwash yarn won’t bloom in the same way when washed as non-superwash, which becomes fuller and develops a slight halo, and is therefore a better choice for colourwork.

Unfortunately, superwash wool is also missing some of the practical characteristics that make wool so wonderful. Once it has been treated it loses a lot of its warmth, and it is no longer as waterproof or elastic. It needs to be washed more often and, as we mentioned above, the polymer coating will eventually break down through washing, so it may still end up felting with time.

Our decision

As with many things, the decision to use superwash or non superwash yarn will depend on a number of different considerations. It might be really important that a garment is easily machine washable, or superwash yarn might give exactly the kind of fabric that you are after. We are certainly not going to judge anybody’s yarn choices!

Here at Flock we have decided not to stock traditional or Chlorine-Hercosett superwash yarns. This is partly because we want to have as little environmental impact as we possibly can, and partly because we love wool in its natural state, and we think treating it in a way that takes away any of its amazing properties is a real shame. We want to work with its wonderful characteristics to celebrate gorgeous squishy cables and beautiful colourwork, and think that learning to care for our garments a little differently absolutely a price worth paying.

All About Superwash Yarn

How does wool become superwash?

What are the benefits of superwash yarn?

And the drawbacks?

Our decision

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