Balsa, a tree of tropical America. Balsa wood is pale in color, so soft it can be dented with the fingernail, and about one-half as heavy as cork. The wood's light weight is explained by the fact that the tree grows continuously; it does not form annual rings and consists only of large, spongy cells. Because of its great buoyancy, balsa wood is used in making life preservers, rafts, floats, and similar articles. It is also used in insulation and—because it is strong in relation to its weight—as a reinforcing material in such fiberglass products as boat hulls. Since it is lightweight and can be easily carved and shaped, it is used in the construction of model airplanes.
The balsa tree is native to the West Indies and northern South America. It reaches a height of 90 feet (27 m) and has a smooth trunk and large toothed or lobed leaves nearly one foot (30 cm) wide. The flowers are white, with petals about five inches (13 cm) long.
The term balsa is applied to rafts made of balsa wood, or to a raft made of two cylinders of metal or wood, having a platform joining them together.
The balsa tree is Ochroma pyramidale of the family Bombacaceae.