IPC-1478 filter paper efficiency was evaluated using polystyrene latex and dioctyl phthalate (DOP aerosols). Efficiency was measured as a function of particle size, filtration velocity, and filter mass loading. Experimental results of 0.557-µm and larger particle sizes indicate that this medium has limited effectiveness under high-velocity and high-loading conditions. Differences in efficiency were observed when this medium was tested with solid and liquid aerosols.