We here present laboratory based experimental and theoretical methods to characterize the filtration efficiency (FE) behavior of diesel particulate filters (DPFs) exposed to soot laden gas streams. Sensitivity of the FE behavior on filter microstructure and geometry properties have been studied, along with the impact of the hydrodynamic and aerosol flow conditions (flow rate, temperature, aerosol characteristics). Evolution of FE with soot load is reported from clean filter FE to maximum efficiency (100%), as the deposited soot in the filter wall itself acts as the filtering medium. The theoretical model considers different mechanisms (Brownian diffusion, particle interception and inertia) of soot capture and their impact on number based and mass based FE. The predictions from the theoretical model are in good agreement with experimental observations over a broad range of filter microstructure. Sensitivity of FE evolution on bare and coated filters has been reported, along with the impact of ash loading of the filters. Methods presented here are useful in determining the performance of DPFs under well-defined laboratory conditions and their extension to dynamic field conditions. These are also useful in determining filter properties for obtaining high FE and low pressure drop. (C) 2010 Elsevier Ltd. All rights reserved.