So, I have this pair of work socks that are 100% wool and I have washed and dried them repeatedly. The results? Stiff tubes of felt that are so difficult to put on that it makes me want to cry. I obviously did not follow the care instructions. But, I have other pairs of wool socks that do great in the washer and dryer. Turns out there is a reason.
Sheep wool is a part of the skin of the sheep. The fibers are covered with "scales"--little pieces of protein arranged over the fiber like the scales of a reptile. All animal fibers have them and the softness of the fibers are directly correlated to how big the scales are. Turns out that when you get a blob wool warm and wet and then agitate it, scales on the fibers all start to interlock with each other acoss the fiber strands. Ever look at a piece of felt? It is a clump of wool where the fibers have become all matted together and trying to pull it apart is an exercise in fulility. It is like that because the scales on the fibers have become interlocked. My socks have clearly turned to felt.
What about my wool socks that are just fine? Turns out there is an industrial process that can be used to treat the wool to prevent felting called Superwash. This is a non-technical explanation--if you need a technical one, you will want to consult industry publications. What Superwash treatment does is remove to scales off of the fibers or what amounts to gluing them down so they can't interlock with each other. There are several different processes to accomplish scale removal--acid washes, polymer coatings and gas treatments. All of these result in wool that is perfectly safe for humans to wear and use. The processes themselves can be toxic to humans and can involve things like cholrine gas, ozone gas, or sulphuric acid. Each process is subject to patent law and simply not something you can do yourself. There actually is not a factory making Superwash wool in the US as the amount of wool needed to make such a facility economically viable is not available in the US. If you purchase Superwash wool products they are probably from Germany, South Africa or China since that is where the Superwash facilites are located. When wool felts it also shrinks, and since shrinkage can be undesirable the Superwash process was invented to combat this. It seems be remarkably effective!
Some other factoids:
--not all washable wool is Superwash
--industry estimates say about 5% of Superwash uses acid methods and 95% use polymer coatings
--wool items made before the early 1970s are never Superwash
--while polymer-treated wool can go in the dryer, the heat from the appliance can cause the polymer to lose some of its effect so air-drying is the best way to dry Superwash items if you want them to maintain their Superwash traits.
Photos are of Madelinetosh DK in "Thunderstorm" and Malabrigo Rios in "Zarzamora", both are Superwash treated wool products