Balsa wood is perhaps best known as a suitable wood for making model airplanes due to its lightness and ease of handling. Thin sheets may even be cut simply with a utility knife. Although it doesn't behave like other hardwoods, balsa is technically in that class. Its name comes from the Spanish word for "raft," alluding to balsa's tendency to float.
Growth and Production
Balsa grows naturally in any tropical, wet environment. It is found most commonly in Central and South American rain forests. It is an especially important export from Ecuador. The wood is grown on plantations, eliminating the need for laborious cutting and hauling of single trees out of the old-growth forests, since the trees do not typically grow in stands. According to Woodworkers Source, sustainably grown operations are in existence for this wood. A plus for plantation-grown stock, balsa grows quite rapidly; it is ready for harvest in about seven years under ideal conditions. Trees grow up to 80 feet high, with a trunk diameter of 30 inches or more. Native trees may attain up to 4 feet of trunk diameter. The wood has no natural resistance to decay, so it should be harvested and used more quickly than other hardwoods.
Why is balsa wood so light? Unlike other hardwoods, balsa wood cells are fatter and contain more water. Only 40 percent of the wood is actually solid because it contains less lignin – the plant "cement" that solidifies wood. It is considered the lightest and softest of the hardwoods. Because of this nature, green balsa wood has to be slowly kiln-dried. The sapwood, which is most often used part of the tree, is white or light brown in color; the heartwood is darker brown or reddish.
Balsa was first identified during World War II as a substitute for cork and is still used for rafts as well as surgical splints, insulation, life belts, floats and toys. Balsa comes in varying densities. The lightest wood, used for model airplanes, weighs usually 6 to 18 lbs. per cubic foot. Denser stock is used for model houses or bridges, or wherever stiffer construction is required.
Balsa is available in three grain patterns depending on the cut: "A grain" is cut on a tangent and has long grain lines. These sheets curve and bend easily and are best used for wrapping components such as model plane fuselages. Because of the long fibers, it also has a tendency to warp. "B grain" is a medium, slightly stiffer product and is random cut. It is used for multipurpose parts. "C grain" is quartersawn, mottled and the stiffest of the three grains. Balsa wood is sold in 3- to 4-foot-long sheets ranging from 1/32 to ½ inch thick. Balsa wood can be easily cut, shaped, sanded, glued, routed and painted. It shows some dulling effect on cutters and so is best worked with sharp, thin-edged hand or power tools.