Contrary to what most people think, most of the weight of a banjo is not from its wooden parts. Rather it is because of all the metal inclusions in it. A typical banjo will have much more metal parts than a typical guitar. It can weigh even more if it has a tone ring. Tone rings are usually made of solid bronze that are denser than steel. You will find this ring around the resonator box in bluegrass style instruments. It is this ring that gives bluegrass banjos their distinctive bright and rich sound characteristics. But there are those banjos that are lighter as well. If you are looking for a lighter instrument, then look for an instrument with an open box design that does not have the tone ring.