Double-network polymers (DN-polymers) are xerogels prepared by the complete freeze drying of double-network hydrogels (DN-hydrogels) polymerized from poly (2-acrylamido-2-methylpropanesulphonic acid) sodium salt and polyacrylamide. The skeleton structures of these polymers exhibit superior mechanical resistance to moisture. This study investigates the static structures of dried-state DN-polymers by determining their porosity from nitrogen adsorption isotherms and mercury intrusion techniques. In addition, the morphologies of the DN-polymers were observed by scanning electron microscopy and laser microscopy. The DN-polymers formed a continuous porous network with diameters ranging from 1.7 nm to more than 100 μm. Three classes of hierarchical porous structure were identified. Small pores (diameter 1.7–10 nm) were present within the frameworks of mid-sized pores (diameter 60 nm), and the mid-sized pores resided in the frameworks of large pores (diameter 4 μm). The DN-polymers possess a fractal-like architecture, which confers both high rigidity and lightweight.