Abstract: A method is provided to prepare a filter material, the method comprising the steps of: providing a porous substrate; preparing a high internal phase emulsion wherein the external phase of the emulsion comprises polymerizable monomers, and the internal phase is a non-polymerizable phase; impregnating the high internal phase emulsion into the substrate felt; and polymerizing the polymerizable monomers. A layer of cured foam as is thereby formed on the substrate and within pore volumes of the substrate. The cured foam can have a high porosity, small pore size, and low density, resulting in a filter material having a high efficiency in removal of particles, at a lower pressure drop than alternative high efficiency filter materials.