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Patagonia Chlorine-Free Wool
Photo: Tetsuya Ohara

On Wool and Chlorine

Chlorine-treated Wool
The surface of wool fibers are covered by small barbed scales. These are the reason that untreated wool itches when worn next to skin. When wool is machine-washed and dried, these scales can become interlocked. As a result, wool is usually dry-cleaned or hand-washed to avoid felting and shrinking.

Machine-washable wool was made possible by the development of a chlorination pretreatment of the barbed scales combined with the application of a thin polymer coating. These treatments make wool fibers smooth and allow them to slide against each other without interlocking. This also makes the wool feel comfortable and not itchy. Millions of pounds of wool are processed each year using this chlorine-based method.

Unfortunately, this process results in wastewater with unacceptably high levels of adsorbable organohalogens (AOX) – toxins created when chlorine reacts with available carbon-based compounds. Dioxins, a group of AOX, are one of the most toxic known substances. They can be deadly to humans at levels below 1 part per trillion. Because the wastewater from the wool chlorination process contains chemicals of environmental concern, it is not accepted by water treatment facilities in the United States. Therefore all chlorinated wool is processed in other countries, then imported.

There are a few alternative processes that remove the tips of the barbed scales without the use of chlorine. Some of these methods use another strong oxidizing chemical, such as ozone or hydrogen peroxide, which in wastewater treatment breaks down into oxygen and water. Patagonia chooses chlorine-free and AOX-free methods to make machine-washable wool garments with next-to-skin comfort.

The Problem with Chlorine
Garments made from chlorine-treated wool do not pose any risk to the consumer. The primary environmental concern with chlorine-treated wool is the industrial wastewater from chlorination facilities. Patagonia’s support of chlorine-free wool is therefore similar to our support of organic cotton. We switched to organic cotton when we learned the environmental costs entailed in its production. Similarly, the environmental impacts of the wool supply chain led to our choosing materials not treated with chlorine.

For more information about chlorine, visit the industry website

For a report from the nonprofit research organization Environmental Working Group about chlorination byproducts, visit

Chlorine-Free Wool Products

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