Abstract: A reticulated hydrophilic foam substrate and bonded active surface particle powder composite filter material is generated by foam polymerization of a prepolymer phase with an aqueous phase. The reticulated hydrophilic foam substrate is characterized by relatively low pressure drop and low resistance to flow through the foam substrate. The prepolymer phase is a hydrophilic polyurethane prepolymer receptive to the aqueous phase for foam polymerization upon mixing with the aqueous phase. The aqueous phase in turn is a pourable and flowable slurry mixture of water, active surface particle powder, and surfactant wetting agent. The aqueous phase includes sufficient water or other evaporable liquid to provide a protective liquid layer or coating over the active surfaces of the powder particles.