Let's put it straight away, “Superwash” is actually a term that comes from English, and it is also the term advised by Termium - one of the references in translation - in French; it corresponds to the trade name of the company IWS Nominee Co. Ltd, still according to the terminology and linguistic data bank 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 in machine up to 30 degrees without risk of felting.
If wool in its natural state is felt, it is because of - 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 it is enough for a rapid drop in the temperature of the water to cause the tightening of the scales ... add soap and you have one of the best ways of felting 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 made it possible to machine-wash wool. How practical!
Certainly, but what does this imply a “Superwash” treatment?
The “Superwash” treatment is not trivial. It consists in immersing the wool in successive baths containing essentially chlorine and caustic soda which together causes a chemical reaction implying thereafter an anti chlorine treatment. This is followed by another treatment which makes it possible to smooth the scales by means of different methods, in particular a polymer bath. As following 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 extended, a bit like a synthetic material ... which is what has become of our wool initially "natural".
If your choice is for "Superwash" wool, it is important to remember that it is more elastic - making a sample is necessary. It is also easier to dye and does little or no pilling.
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.