A Cornish Rex is a breed of domestic cat. The Cornish Rex has no hair except for down hair|down. Most breeds of cat have three different types of hair in their coats: the outer fur or "guard hairs", which is about 5 cm long in shorthairs and 10cm+ long in longhairs; a middle layer called the "awn hair"; and the down hair or undercoat, which is very fine and about 1 cm long. Cornish Rexes only have the undercoat. The curl in Cornish Rex fur is caused by a different mutation and gene than that of the Devon Rex.