It's an old world garment skill where 100% wool is processed to make felt. The favorite wool sweater you wanted to wear next Christmas but was washed in hot water by mistake, is now a felted garment and little frou-frous favorite outdoor garment. 

Felt hats are a favorite with men and women and have been a part of fashion for a long time. Wet felting is synonymous with boiled wool used for jackets and involves 100% wool, a lot of hot water and washing machine agitation to make felt.

Dry felting is used  for adding adornments and designs to garments by impressing roving wool with sharp, spiked needles into the garment.