We present here a methodology to produce highly porous cross-linked hydrogel materials by templating concentrated CO2-in-water (C/W) emulsions. Poly(vinyl alcohol) (PVA), blended PVA/PEG, and naturally derived chitosan materials were produced via this route. The technique can be carried out at moderate temperatures and pressures (25 degrees C, < 120 bar) using inexpensive hydrocarbon surfactants such as PVAc-based block copolymers which are composed of biodegradable blocks. This methodology opens up a new solvent-free route for the preparation of porous biopolymers, hydrogels, and composites, including materials which cannot readily be produced by foaming.