BALSA, the name given to a tree (Ochroma lagopus) of the bombax family (Bombaceae), called also corkwood, native to tropical South America, and noted for its exceedingly light wood (Span. balsa, a raft or float). In appearance the tree is somewhat like the North American cottonwood (Populus deltoides), while the wood resembles clear white pine (Pinus Strobus) or basswood (Tilia americana), and has a velvety feel. Well-seasoned com mercial balsa wood, which weighs only 7 lb. to 8 lb. per cu.ft. is the lightest wood known. Because of this extreme buoyancy, about twice that of cork, it is admirably adapted for making floats for life lines and life-preservers. Its resiliency makes it an excellent shock-absorbing material for packing pianos, finely finished furniture and similar articles, and also for foundation pads for machinery. On account of its insulating properties, it is extensively used for lining incubators, refrigerators and cold storage rooms. Its lightness combined with high insulating power renders it extremely valuable as a material for constructing the various containers used in dry-ice transportation. It is also em ployed in the construction of passenger compartments for aero planes. (See CORKWOOD ; DRY-ICE.)