Novel microporous polymers in forms ranging from films to blocks and intricate shapes from synthetic thermoplastic polymers, such as, olefinic, condensation, and oxidation polymers, are disclosed. In one embodiment the microporous polymers are characterized by a relatively homogeneous, three-dimensional cellular structure having cells connected by pores of smaller dimension. Also disclosed is a process for making microporous polymers from such thermoplastic polymers by heating a mixture of the polymer and a compatible liquid to form a homogeneous solution, cooling said solution under non-equilibrium thermodynamic conditions to initiate liquid-liquid phase separation, and continuing said cooling until the mixture achieves substantial handling strength. Also disclosed are microporous polymer products which contain relatively large amounts of functionally useful liquids and behave as solids.