Gradient nanofiber filter media

A composite filter media comprising multiple layers of media material, wherein:

• the composite filter media comprises at least one nanofiber layer that comprises polymeric media material having a geometric mean fiber diameter of less than 1 μm;
• the composite filter media has a pore size distribution such that P99/P50 is less than 2, wherein P50 and P99 are the pore sizes such that 50% and 99%, respectively, of a total flow passes through pore sizes equal to or smaller than P50 and P99;
• and the composite filter media comprises a microfiber layer upstream of and adjacent to the nanofiber layer, the microfiber comprising microfibers such that the ratio of the geometric mean diameter of fibers at the downstream face of the microfiber layer to the geometric mean diameter of fibers at the upstream face of the nanofiber layer is between 1.2 and 2.8.