In Chinese painting and calligraphy, the brush pen (mao pi) has been the tool of choice since ancient times (for at least 3,000 years) and is one of the "four treasures of the study" (wen fang szu pao), along with the inkstick, paper, and inkstone. Unlike fountain pens, ballpoint pens, and other typical Western metal-pointed writing instruments, brush pens are made from fine, soft animal hair. The quality of the lines created, whether sharp-edged or blurred, thick or thin, depends on the special characteristics of the brush pen and the hair fibers selected.

Typically, brush pen fibers are taken from weasels or sables (brown, white or yellow), Chinese Angora rabbits (white, black or brown), or goats (white, brown or red). Chinese goat hair brushes, known as yang hao, are soft, flexible, and absorbent. The other two types are known as "wolf hair" or lang hao (the weasel hair brush) and "purple hair" or tzu hao (the rabbit hair brush). In some cases, the Chinese artist or calligrapher will combine hair from two different animals in one brush (chien hao) to achieve a balance between different line textures. In some Chinese provinces, in addition to the three traditional sources of fiber, hair from oxen, civets, wolves, horses, rats, mice, sheep and other animals account for more than 40 varieties of brush pens.

Chinese goat hair, typically white in color, is glued into a bamboo handle. New brushes are stiffened with glue or sizing, and often a bamboo or plastic cap protects the bristles. Before using a new yang hao, the bristles must be soaked to remove the sizing. Chinese brush pens, including goat hair ink brushes, tend to be larger than typical Western watercolor paintbrushes because the mao pi can be loaded with several colors at one time for silk painting or calligraphy. Although brown and red goat hair is used for writing brushes, extra long white goat hair fibers make the finest calligraphy tools. Other uses for Chinese goat hair fiber are for the cashmere wool of fine sweater fame.