The next critical parameter to consider is electrical isolation. The only truly conductive TIMs are those based on graphite. Gap fillers based on silicone or non-silicone are generally considered to be electrically isolating. PCMs and greases, however, are not rated as either conductors or insulators. If applied thick enough, they can provide some degree of isolation; although, if voids are present in the material they could provide a route for short circuits, possibly causing catastrophic component failure.