Region: Westchester County, New York State
Message: Hi,

I'm trying to find out more about "super wash" wool.  For a stash busting project, I'm thinning of using my wool and cotton scraps for bird's nests...but am concerned that superwash wool is not a "natural fiber" once it is superwashed.  Your site is the only reference I've found that speaks to its naturalness after superwash treatment,  but it was a brief reference. Do you have any more information?

You're probably referring to my page answering the question, "Is there some way to make my own Superwash Wool?". The main reason why I want to discourage attempts to make Superwash wool at home is that it is dangerous to work directly with chlorinating chemicals under the acid conditions required by wool. That is not an issue after the treatment is complete, however.

It's true that wool is not completely natural after it has been given the Superwash treatment. The question is, is there any reason why this should matter for your project? Is Superwash wool safe for birds to be exposed to?

The vast majority of commercially available Superwash wool has been chlorinated and then treated with a sort of plastic, a polymer resin called Hercosett 125, that glues down the scales that are found on the surface of mammalian hairs (like the scales on our own hair); this enables the wool fibers to be treated roughly without interlocking, shrinking, and felting. Hercosett 125 is a polyamide-epichlorohydrin polymer. While the chemicals that comprise this polymer are themselves highly toxic, that does not mean that the polymer itself is. Many plastics that are harmless once combined together into long chemical chains are made from smaller molecules that are toxic before they are combined. However, I can't find any information on the safety of Hercosett-treated wool. It certainly appears to be non-irritating to wear as clothing, so it's probably okay for bird nesting material.

Since Superwash wool is coated with plastic, you really can't consider it a 100% natural fiber. Let's put it into the same category as synthetic fibers, or wrinkle-free cotton, (which is treated with formaldehyde-containing resins) or any stain-resistant natural-fiber fabric (which is coated with Teflon). If you have a personal rule of not using any synthetic fiber for this project, such as polyester, then don't use Superwash wool. It is chemically treated and plastic-coated, so it doesn't quite belong in the same category as untreated natural wool or cotton, although it feels nice, and it certainly does dye beautifully with the same dyes used on natural wool.

Since birds do not actively eat yarn, they will consume only tiny traces of whatever chemicals are in the wool. I think it's probably more important to avoid giving them mothproofed wool, because the treatments used to make wool mothproof are pesticides which kill insects. They are listed as having "low mammalian toxicity", but that may or may not go along with low avian toxicity. I don't know how much of the commercially available wool supply is mothproofed, nor how to tell whether the wool you have has been treated with mothproofing.

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