Carborane acid consists of 11 boron atoms; each boron atom is bound to a chlorine atom. The chlorine atoms serve to enhance acidity and act as shields against attacks from the outside due to the steric hindrance they form around the cluster. The cluster, consisting of the 11 borons, 11 chlorines, and a single carbon atom, is paired with a hydrogen atom, bound to the carbon atom. The boron and carbon atoms are allowed to form six bonds due to boron's ability to form three-center, two-electron bonds.
Although the structure of the carborane acid differs greatly from conventional acids, both distribute charge and stability in a similar fashion. The carboranate anion distributes its charge by delocalizing the electrons throughout the 12 cage atoms. This was shown in a single crystal X-ray diffraction study revealing shortened bond lengths in the heterocyclic portion of the ring suggesting electronic delocalization.
The chlorinated carba-closo-dodecaborate anion  is an outstandingly stable anion with what has previously been described as "substitutionally inert" B–Cl vertices.  The descriptor closo indicates that the molecule is formally derived (by B-to-C replacement) from a borane of stoichiometry and charge [BH] (n = 12 for known carborane acids). The cagelike structure formed by the 11 boron atoms and 1 carbon atom allows the electrons to be highly delocalized through the 3D cage (the special stabilization of the carborane system has been termed "σ-aromaticity"), and the high energy required to disrupt the boron cluster portion of the molecule is what gives the anion its remarkable stability. Because the anion is extremely stable, it will not behave as a nucleophile toward the protonated substrate, while the acid itself is completely non-oxidizing, unlike the Lewis acidic components of many superacids like antimony pentafluoride.  Hence, sensitive molecules like C can be protonated without decomposition.