Common names for the genus include silk cotton tree, simal, red cotton tree, kapok, and simply bombax. In Chinese they are known as Mumian (Chinese: 木棉; pinyin: mùmián), meaning "tree cotton". Currently four species are recognised, although many plants have been placed in the genus that were later moved.
The genus is best known for the species B. ceiba, which is widely cultivated throughout tropical and sub-tropical regions of the world. It is native to southern and eastern Asia and northern Australia.
Bombax species are among the largest trees in their regions, reaching 30 to 40 metres in height and up to three metres in trunk diameter. The leaves are compound with entire margins and deciduous, being shed in the dry-season. They measure 30 to 50 cm across and are palmate in shape with five to nine leaflets. The calyx is deciduous, meaning it does not persist on the fruits. They bear five to ten cm long red flowers between January and March while the tree is still leafless. The stamens are present in bundles in two whorls, while the staminal column lacks lobes. The ovary matures into a husk containing seeds covered by a fibre similar to that of the kapok (Ceiba pentandra) and to cotton, though with shorter fibres than cotton, that does not lend itself to spinning, making it unusable as a textile product.