There are many types of wood labeled as lite, or light, plywood. I use a great deal of Italian Poplar bending plywood in my designs which is the very light colored 3-ply stuff that you generally see advertised as light ply from places like Balsa USA. It does not contain any balsa nor does it vary in weight and density like balsa does. I love the stuff for a number of reasons, the two biggest being that it can be obtained in 4' x 8' sheets and also because it laser cuts very nicely. The larger sheets means no edge gluing or splicing to make large parts as you would have to do with balsa. Judicious use of lightening holes, made simple by laser cutting, can get the weight down close to what you would have with balsa wood and it is still stronger. It also happens to be much cheaper than balsa. I know many folks hate the stuff but I happen to like it and have used it quite successfully in a number of designs. My .02 cents.