According to one embodiment, a nonwoven fiber mat includes between 10% and 50% by weight of a plurality of first glass fibers having an average diameter of less than 5 μm and between 50% and 90% by weight of a plurality of second glass fibers having an average diameter of greater than 6 μm. The nonwoven fiber mat also includes an acid resistant binder that binds the first and second glass fibers together. The nonwoven fiber mat has an average pore size of between 1 and 100 μm and exhibits an air permeability of below 100 cubic feet per minute per square foot (cfm/ft2) as measured by the Frazier test at 125 Pa according to ASTM Standard Method D737.