Cellular metals have ranges of thermomechanical properties that suggest their implementation in ultralight structures, as well as for impact/blast amelioration systems, for heat dissipation media and in acoustic isolation. The realization of these applications requires that the properties of cellular metals be understood in terms of their manufacturing constraints and that their thermostructural benefits over competing concepts be firmly established. This overview examines the mechanical and thermal properties of this material class, relative to other cellular and dense materials. It also provides design analyses for prototypical systems which specify implementation opportunities relative to competing concepts.