Open pore polyurethane (OPP) is a new and unique column filling material for gas and liquid chromatography (LC). Columns are prepared by filling tubing with isocyanate and alcohol monomers in solution and permitting these monomers to polymerize within the tubing. The resulting material is a rigid cross-linked gel which can be used directly to perform chromatographic separations, or reacted at chemical sites to form columns of differing functionality. The chemical and physical stability of urethane, coupled with the ability to change porosity and functionality, make OPP a nearly ideal support for liquid chromatography.