Boomex is a high-explosive material commonly used in demolitions. It is similar to plastic explosives such as C-4, with the addition of nanites that allow the boomex to mold itself into desired shapes; creating boomex requires the use of nano-assemblers. On rare occasions, generally involving a well-equipped madman, boomex is doped with fullerened antimatter for increased yield.
That last bit bears further examination. According to the comics, boomex is fully nitrated buckminsterfullerene, with a molecular formula of C70 N70 O210 (assuming "fully nitrated" means ONO2 groups like nitroglycerine has rather than the NO2 groups more common in high explosives), molecular weight of around 5180. At first glance it seems like we might expect to be able to compare it, thermodynamically and energetically speaking, to the theoretical explosive compound octanitrocubane, which we believe would have more snap to it than TNT, weight for weight, but not enormously more,
But at the ratio, quoted from the comics, of one single antiproton held inside each fullerene shell, held in the center by mutual repulsion from the electron cloud until the molecule breaks down and it is no longer confined, every kilogram of this stuff has, well, round it off to 193mg of antimatter in it. According to the textbooks 193mg of antimatter annihilating with an equivalent mass of normal matter releases about 3.5 times ten to the thirteenth joules of energy, which comes out to a bit under eight and a half kilotons of TNT. Antimatter-doped boomex is scary stuff, and I'm not sure how you'd even make use of its exotic properties. Its brisance would be far, far off the charts. I'm not clever enough to use it to make a shaped charge--one imagines a tiny hollow needle of depleted uranium a kilometer long stuck inside an even longer spaghetti noodle of antimatter doped boomex, turning inside out and going that-a-way upon detonation, some small portion of it achieving a few percent of c. ("Kaboom?" "Yes, Rico. Kaboom.")