Let's get things straight straight away, “Superwash” is indeed a term that comes from English, and it is also the term recommended by Termium - one of the references in terms of translation - in French; it corresponds to the trade name of the company IWS Nominee Co. Ltd, still according to the terminology and linguistic database of the Government of Canada.
So that some call it untreated, anti-felting or other, I will speak here of "Superwash" even if it is the same product: a treatment received by the wool which allows it, in principle, to be washed. machine up to 30 degrees without risk of felting.
If wool in its natural state felt, it is because - or thanks - to its composition. The surface of each fiber is covered with scales. However, under the effect of heat, the scales open. The friction of these fibers between them then causes their permanent intertwining, then a rapid drop in the temperature of the water is enough to cause the scales to tighten ... add soap and you have one of the best ways to felt wool : to remember for all your felting projects!
With the development of washing machines, it was therefore almost necessary, in the 70s, to find a treatment - Superwash - which allowed wool to be machine washed. How practical!
Sure, but what does "Superwash" treatment involve?
The "Superwash" treatment is not trivial. It consists of immersing the wool in successive baths containing mainly chlorine and caustic soda which together causes a chemical reaction subsequently involving an anti-chlorine treatment. Another treatment follows which smooths the scales by means of various methods, in particular a polymer bath. As after all these treatments the fiber is damaged and has lost its softness, it is subjected to a new softening bath this time.
Another process, that of Kroy-Ercosett, combines chlorine and resin. The thread is transformed; it becomes thinner, not swelling and round.
But according to some, after these treatments the longevity of the fiber would be prolonged, a bit like a synthetic material… what moreover became of our initially “natural” wool.
If your choice is "Superwash" yarn, it is important to remember that it is more elastic - sample is required. It is also easier to dye and little or no pills.
If you prefer natural wool, you will have to wash it by hand, cold and dry it flat ... which is in any case advised with all wool dyed by hand.