The traditional Hercosett superwash treatment is very effective.  By superwash treating wool, the edges of the scales on each hair are removed and smoothed, so that they cannot catch together as well.  This prevents shrinking and felting when the wool is washed in hot water or agitated.  The treatment itself uses plenty of chlorine and is therefore of questionable environmental credentials.

After the advent of cotton and polyester fibres, and with the early washing machines, wool became seen as "too difficult" because, with life speeding up, everyone expected to wash everything in the machine and wool did not respond well to the heat and agitation.  Hand washing was seen as a chore which took too long.  So superwash treatment of wool was a break-through in terms of bringing back wool into popular usage.