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 mu m. 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 mu m). The DN-polymers possess a fractal-like architecture, which confers both high rigidity and lightweight. (C) 2016 Elsevier Ltd. All rights reserved.