Abstract: The present invention relates to a novel process for forming metal matrix composite bodies. Specifically, in a particularly preferred embodiment for making metal matrix composite bodies by a spontaneous infiltration technique, an infiltration enhancer or an infiltration enhancer precursor or an infiltrating atmosphere are in communication with a rigidized filler material or a rigidized preform, at least at some point during the process, which permits molten matrix metal to spontaneously infiltrate the rigidized filler material or riigidized preform. A structural refractory material which holds the preform is made by forming a first precursor to the supportive structural refractory material and subsequently causing the precursor to become a rigid supportive structural member. Such spontaneous infiltration occurs without the requirement for the application of any pressure or vacuum.