Machine Washable Wool: The good, the bad and the ugly. - Nui Organics Skip to content

Save 50% on Organic Cotton Waffle. code WAFF50


Machine Washable Wool: The good, the bad and the ugly.

The Structure of Wool

Wool belongs to the group of proteins called keratin. It is naturally elastic, resilient and absorbent.  It has a scaly outside surrounding an inner core. The scaly outside is ‘hydrophobic’, meaning it repels water. The inner core, however, is ‘hydrophilic’, which means it readily absorbs water.

This hydrophilic core gives the wool it’s ability to absorb around 30% of it’s weight in moisture, without feeling wet. This is because the water remains on the inside and what you’re touching is the hydrophobic water-repellent surface.

This structure also gives wool fibre the ability to transport water. If you’re sweating for example, it can wick moisture away from the skin and release it into the atmosphere.

It also dries quickly and does not retain smells.  This unique fibre structure means sheep can tolerate exposure to light rains and stay waterproof as well as tolerate extreme ranges in temperature.  Wool can decompose in soil within a year, releasing the natural fertilising nitrogen nutrients back into the earth, and is fully renewable, regrowing on the sheep every year.

When these scaly wool fibres rub against each other and with the addition of moisture and sudden changes in heat, like what happens in a washing machine, the scales cling onto each other (think ‘Velcro’) and felting occurs.   Repeated felting results in the wool shrinking as it all binds together.

But life is busy and who wants to handwash every piece of wool... So in the 1970's Superwash wool was born.

Merino Wool

Meet Superwash...

In order to make wool machine washable, the natural scales are stripped using a chlorine treatment.  After stripping the scales off, a thin polymer coating is applied. This allows the fibers to slide against each other without felting and shrinking. This is called the ‘Chlorine-Hercosett Treatment’ and at least 70% of all Superwash yarn is produced this way.  Seems like a great idea, so why is that bad?

Wool treated with Chlorine

Environmental Impact

As a start, this ‘Chlorine-Hercosett Treatment’ uses large amounts of water as well as dangerous substances, leading to significant pollution of wastewater.

Toxic chemicals

Chlorine and polyamide-epichlorohydrin resin are highly toxic. In addition, a natural reaction happens between the chlorine and the carbon compounds of the wool creating high levels of adsorbable organohalogens (AOX). Dioxins, a group of AOX, are one of the most toxic substances known. They can be deadly to humans at levels below one part per trillion. Wastewater from the wool-chlorination process contains such high concentrations of chlorinated chemicals, that most wastewater treatment facilities in the United States do not accept it. Which is why most chlorinated wool is processed in other countries.

Wool processed this way does not pose any threat to the wearer, but every person who has had contact with that wool during the process of Superwash is exposed to those toxins, as well as them being discharged in the wastewater and so into the environment of the countries which do allow for this process. 

Plastic Free Ocean

How does Superwash affect the wool?

Water Resistance

With the hydrophobic scaly surface no longer present, the fibre loses its ability to repel water. It also cannot transport moisture as effectively. The absorbent hydrophilic core is still present, but what you’re actually touching is not natural wool. It is instead this new synthetic coating.  So that means not only is it less waterproof, but is also less able to transport moisture away from the skin.

Warmth & Elasticity

Superwash wool is not as warm or elastic as non-Superwash wool. By flattening the scales and essentially gluing them down with resin, the wool no longer traps heat and air. Garments made with Superwash yarn also stretch out after a while, because the fibre no longer has any scales to cling onto, so garments will no longer hold their shape.

What’s the Alternative?

Most brands use Superwash yarn because it is the cheapest, fastest way to render wool machine washable.  

Because the process is so very toxic, and many of the natural benefits, like water resistance,  warmth and elasticity are compromised, there is a growing effort to find alternatives.  Ozone and hydrogen peroxide both break down into oxygen and water when the waste water is treated and these methods are in use.  There is also the EXP Treatment by European company Schoeller Group that uses natural salts and ecological polymer micropatches. 

What does Nui use?

Our merino thermals and merino silk are made with GOTS certified organic merino wool. Certified organic from farm to finished product our merino is made machine washable using  Naturetexx® Plasma technology.

No chlorine, just air and plasma. This revolutionary process, powered by renewable energy, is the ecological alternative to chlorine-based chemical treatments for wool.  The ‘Tesla’ of machine washable wool, the process uses plasma instead of chlorine to modify the wool fibre surface. The process is free of chemicals and takes place in a dry state without water.

How does it work?

A plasma field is generated by discharging voltage between two electrodes in a controlled and consistent manner. Carefully prepared wool passes through the plasma field where electrons and ions in the plasma interact with the wool fibre. They permanently modify the wool top’s surface and even out the wool fibre’s scales. The wool is then spun into yarn.  Final garments are machine washable without felting and shrinkage.

It is certified by OEKO-TEX®, bluesign® and for organic use by GOTS and IVN Best.

What's next?

We hope that chlorine treated plastic coated wool will become a thing of the past. For that to happen the demand for cleaner chlorine free processing needs to come from the consumer. That’s you. Ask brands that use Superwash wool to change. Did you even know that’s how they got machine washable wool? Share what you know. Education is key. Support brands that go the extra mile and incur the extra costs to bring you wool that’s cleaner and safer from start to finish.   

Shop Chlorine Free Wool
Merino Wool: The Unsung Hero of Summer Apparel
Cool Comfort: The Summertime Bliss of Kids Sleeping in Merino
Our 'Give Natural, Not Plastic' Gift Guide.