The Black Welsh Mountain is the only completely black sheep breed in Britain. It was developed in the mountains of Wales from black sheep that occurred in the Welsh Mountain breed, which is white. About a century ago, Welsh shepherds began to breed the black sheep together, also selecting for a finer fleece and improved body conformation. The resulting breed, also known by their Welsh name, Defaid Mynydd Duon, was recognized in 1922 with the establishment of the Black Welsh Mountain Sheep Society.

The Black Welsh Mountain sheep wool is known for its short, thick, and densely stapled characteristics. The wool is typically deep black, with a slight reddish cast, and has a staple length of 28-36 microns. This wool is suitable for various textile applications, including cardigans, jackets, and woven fabrics. The wool is also known for its ease of spinning experience and is relatively easy to process and work with. It is almost completely free of kemp and has significant crimp, which blends together in a mass except at their slightly pointed tips. The wool is usually durable, light, and warm, making it an attractive choice for handspinners and other textile enthusiasts.