from wikipedia

Wool felt and felted wool are similar to boiled wool, all of these processes date back to at least the Middle Ages. The word felt itself comes from West Germanic feltaz
Felt is a non-woven cloth that is produced by matting, condensing and pressing woollen fibres
alls i know is that its usually thick. not sure if its itchy but my boiled wool stuff isnt. does cos have a crew/round neck version of that?