This invention relates generally to a novel method of manufacturing a composite body. More particularly, the present invention relates to a method for modifying the resultant properties of a composite body, by, for example, minimizing the amount of porosity present in the composite body. Additives such as TaC, ZrC, ZrB.sub.2, VC, NbC, WC, W.sub.2 B.sub.5 and/or MoO.sub.2 B.sub.5 can be combined with a boron carbide material which is thereafter reactively infiltrated by a parent metal. The composite body comprises one or more boron-containing compounds (e.g., a boride or a boride and a carbide) which is made by the reactive infiltration of molten parent metal into the boron carbide mass. Particular emphasis is placed upon modifying the properties of a ZrB.sub.2 -ZrC-Zr composite body. However, the methods disclosed in the application are believed to be generic to a number of parent metals and preform materials.