In this work, we report an innovative mechanism, the Kirkendall effect, in creating three-dimensional (3D) microporous catalysts with tunable pore sizes for the growth of hierarchic ultrathin graphite foams (HP-UGFs) with unique properties. Employing the Kirkendall effect is one of the first demonstrated for fabricating 3D porous catalysts, where tunable pores of 1.9–8.3 μm are created on 3D interconnected struts (∼100 μm). With the catalysts, we readily synthesized freestanding HP-UGFs that offer higher crystallinity and electric conductivity, larger surface area, as well as enhanced electric invariance to strains compared to those of conventional ultrathin graphite foams. A gauge factor as low as ∼10 at a strain as high as 80% is achieved owing to the unique porous corrugations created on the microstruts of the HP-UGFs. This work may inspire a new paradigm in designing and synthesizing a new type of 3D porous architecture made of 2D materials with controlled local corrugations, which could greatly benefit flexible electronics.