Let's get this straight, "Superwash" is actually a term that comes from English, and it is also the term recommended by Termium - one of the references in translation - in French; it corresponds to the trade name of I.W.S Nominee Co. Ltd., again according to the Government of Canada's terminological and linguistic database.
So as some call it untreated, anti-felting or whatever, I will speak here of "Superwash" even if it is the same product: a treatment received by the wool that allows it, in principle, to be machine-washed up to 30 degrees without the risk of felt.
If wool in its natural felt state, 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 causes them to become permanently intertwined, so it is enough to quickly lower the temperature of the water to cause the scales to tighten... add soap and you have one of the best ways to felt wool: remember for all your felting projects!
With the development of washing machines, it was almost necessary, in the 1970s, to find a treatment - Superwash - that allowed washing wool in a machine. How practical!
Sure, but what does this mean for a "Superwash" treatment?
The "Superwash" treatment is not insignificant. It involves plunging the wool into successive baths containing essentially chlorine and caustic soda which together causes a chemical reaction that eventually involves chlorine treatment. This is followed by another treatment that smoothes the scales using different methods, including a polymer bath. As a result of all these treatments the fiber is damaged and has lost its softness, it is subjected to a new bath softening this time.
Another process, kroy-Ercosett, combines chlorine and resin. The thread is changing; it becomes thinner, non-inflating and round.
But according to some, after these treatments the longevity of the fiber would be prolonged, much like a synthetic material ... what has become of our originally "natural" wool.
If your choice is superwash, it is important to remember that it is more elastic - making a sample is necessary. It is also easier to dye and it does not bulge or little.
If you prefer natural wool, you should wash it by hand, cold and dry it flat... which is recommended anyway with all the wools tinted by hand.