The Yak is a domesticated animal originating from Tibet.  Yak wool outperforms traditional wools in many areas.  Yak is known for its warmth, softness and breathability.  It's softness is often compared to that of cashmere.  Compared to traditional wool, Yak is believed to be warmer than merino and has a greater degree of breathability in garments knitted with it.   It also has some wicking properties as well.