My friend Caroline has made this fantastic scarf using woolen knitting yarn, merino and snippets of other fibers. I still dream about it and would love to make similar one.
Today on my short trip to the town I learned this (from the owner of a small haberdashery): not all the woolen knitting yarns are suitable for felting!!! Alas! The ones which are have it written on a label (I saw it: “suitable for felting”), the rest might or might not felt. The least probable to felt are those which altghough 100 % wool are machine washable. Producers treat them with some chemicals to prevent shrinking and felting, which I am sure, knitters like.
Now I understand why an old cardigan I bought in a charity shop retained the original shape after I washed it in the washing machine at 60 degrees full cycle.