A stringed musical instrument body is formed using injection molded high density polystyrene foam with a foaming agent. It is injection molded by itself or around a wooden core to make the body or to form two panels adhered together to sandwich a wooden core therebetween. The core provides good wood tone and the polystyrene with a foaming agent produces good sustain and a resonance of about twenty-eight seconds. A metal reinforced injection molded neck resists warping.