A Cornish Rex is a cat with no hair except 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 'awnhair', and finally the downhair or the undercoat, which is very fine and about 1 cm long. Cornish Rexes have only the undercoat.

The coat of a Cornish Rex is extremely fine and soft to the touch. These cats like to hang around light bulbs, tops of computer monitors, and other warm places.

The Cornish Rex cat breed is a genetic mutation that originated from a litter of kittens born in the 1950s on a farm in Cornwall, England (hence their name). One of the kittens, Kallibunker, a cream colored male, had an extremely unusual fine curly coat, and he became the first Cornish Rex.

The word "Rex" for short or otherwise unusual fur comes from a rabbit breed. King Albert of the Belgians entered some short-haired rabbits in a rabbit show. The rabbits didn't meet the breed standard, but not wanting to offend the king, the people running the show let them in and wrote "rex" by their names.

There is another very similar breed - the Devon Rex. Devon and Cornish Rexes are produced by different genes, and crosses between the two are not allowed in pedigrees.

Cornish Rexes also have a cheesy smell peculiar to the breed.

Another hair-deficient breed is the Sphynx cat.