Compositions capable of exothermic reaction in the condensed state are prepared by pressing a mixture of powders comprising a reactive metal such as titanium, boron carbide and, optionally, carbon (e.g., graphite and/or lampblack) and boron. With moderately fine particle size of boron carbide (about -400 mesh), sustainer compositions are formed. With considerably finer particle size of boron carbide (about -800 mesh), booster compositions are formed. A preferred composition consists essentially of about 67 to 79% titanium, about 13 to 30% boron carbide, up to about 10% carbon and up to about 10% boron.