Balsa woodBalsa is another commonly used core wood. It was first used in 1940s in flying boat hulls. It exhibits very low density (for a wood) and some water resistance. It also provides good thermal insulation and good acoustic absorption. It is easily formed with simple equipment. However, balsa wood has very high minimum density, 100 or 200 kg/m3 is a typical quality, so it is often used where weight saving is not highly required.