Monodisperse packed beds have long been used as surrogate models to predict the filtration performance of particulate filters using analytical methods. In recent years, however, polydisperse packed beds have received special attention as they have the potential to better represent the microstructure of porous filter walls. In this paper, an analytical model for the filtration performance of clean polydisperse packed beds is derived based on the well-proven classical packed bed filtration theory. Predictions of the newly developed model were compared to the results of numerical simulations of the filtration performance of two polydisperse packed beds. The proposed filtration model was in considerably better agreement with the simulations than previous analytical models.