A multiscale carbon substrate is fabricated by growing carbon nanotubes (CNT) on multicellular graphitic foam using an intermediate oxide nanolayer. Abundant CNT growth is seen on the surface throughout, including the walls of inner pores. The Brunauer–Emmett–Teller (BET) technique with nitrogen has been used to measure the specific surfacearea (SSA) of this multiscale structure. It is seen that attachment of CNT provides over a one hundred fold increase in usable SSA of the material with negligible increase in volume and a weight gain of only 2.5%. These results correlate well with semi-empirical predictions obtained by combining analytical modeling and microstructural data.