Machine Washable Wool


Wool is durable and resilient.  The molecular structure of wool means that it can be stretched 50% of it’s length when wet, and 30% when dry, and still return to it’s original shape. Bend a wool fibre up to 20,000 times on itself; it still won’t break.  It is flame resistant, and hygroscopic (takes up moisture) so it is great for both cool and hot climates. In fact, it seems to be the perfect fibre.  BUT- it has to be treated like a queen, especially when washing.

The outer layer of each individual wool fibre consists of scales that interlock with the fibres around them, and this interlocking, we know as felting.  In many circumstances, felting/shrinkage is a desired characteristic – it can create a softer finish for a woven fabric, is ideal for shaping (hats, for example) and felted wool batts have many industrial uses.  Billiard tables use lovely fine- micron felted fibre batts – even if the billiard  green does seem more like a bilious green at times. (I do see they now make tables with different coloured felts, maybe I wasn’t the only one who found the green a bit bright).

However, one of the disadvantages of untreated wool is the extra care that it requires. You can’t just throw an untreated vest or jumper in the washing machine, and have it come out the same way it went in!  Felting of fibres is virtually irreversible, without some damage to the fibres.

Enter machine washable wool, also known as shrink resistant wool or, Superwash wool.

Machine Washable wool has been either treated with acid to remove part of the scales that cause the felting or, far more commonly  has been coated with a polymer to prevent fibre migration; that is, to stop the fibre from interlocking with the fibres around it.  This coating process -Sirolan BAP – is more commonly known as “Superwash” -and was invented by our very own CSIRO here in Australia.

Now to be honest, the superwash treatment is really quite a harsh treatment. The process, and the  residue produced as a result of treatment is not particularly nice.  But compared to what happens in the cotton processing industry, it’s not quite so bad. And the wool itself, after treatment, is not toxic.

Most superwash treatment is now done outside of Australia, (quite a lot in China),and other than cost, it is one of the reasons that so much Australian fibre heads overseas.  It may well return to us in yarn or as tops, but generally if it is machine washable, that process will have been applied outside Australia.

There are plenty of upsides to treated wool.

Machine washable, or treated, wool takes dye very well, and generally the end result is a more evenly dyed product.  Many commercial wool dyes are made specifically to work with treated wool.

It’s fantastic to use for blending, eg wool/acrylic  or wool/nylon mixes (such as  Platypus Sock Yarn).

Treated yarns generally have a softer feel than untreated yarns, so a knitted garment will feel much softer than an untreated equivalent garment.   (This is not quite the same for fibre however, there are some gorgeously soft fibres grown in Australia).

And of course, it is machine washable, so you can gift a treated garment without having to worry about whether or not the recipient knows how to care for it properly.

Sometimes, when I am looking at yarn, I am very surprised to see that some yarn-makers don’t specify clearly enough whether the yarn is treated or untreated. It’s an important omission, it could mean the difference between a cardigan that fits Little Miss Six perfectly, and the same cardigan fit only for Little Miss Six’s dolly.

And it may mean the difference between smiles and tears.




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