Kapok (Ceiba pentandra) is a tropical tree of the order Malvales and the family Malvaceae (previously separated in the family Bombacaceae), native to northern South America, Central America and the Caribbean, and (as the variety C. pentandra var. guineensis) to tropical west Africa. The word is also used for the fibre obtained from its seed pods. The tree is also known as the Java Cotton, Java Kapok, or Silk-cotton tree. Also referred to as Ceiba, it is a sacred symbol in Maya mythology.

The tree grows to 60-70 m tall and has a very substantial trunk up to 3 m in diameter with buttresses. The leaves are compound of 5 to 9 leaflets, each up to 20 cm and palm like. Adult trees produce several hundred 15 cm seed pods. The pods contain seeds surrounded by a fluffy, yellowish fibre that is a mix of lignin and cellulose. The process of harvesting and separating the fibre is labour-intensive and manual.

The fibre is light, very buoyant, resilient, highly flammable and resistant to water. It cannot be spun but is used as a filling for bedding and upholstery, and for insulation. It was previously much used in life jackets and similar devices. The fibre has been largely replaced by man-made materials. The seeds produce an oil used locally in soap and that can be used as fertilizer.

The commercial tree is most heavily cultivated in Asia, notably in Java (hence its nicknames), Malaysia, and Indonesia, but also in the Philippines, and South America.

A similar fibre is found in the Indian Bombax malabarica, it is termed Indian kapok and is darker in colour and less buoyant than the true variety.