In this work, 3D filtration modeling utilizing realistic SEM image-based 3D structure model, transition/free molecular flow regime, Brownian diffusion, particle-fiber interactions, aerodynamic slip and sieve has been proposed and used for different polyurethane nanofiber-based filters. For the model validation purposes, two polyurethane nanofiber layers prepared by the electrospinning process (having identical average fiber diameter, 120 nm, but different average pore sizes) were combined to form two pairs of nanofiber-based filters; each pair consists of two filters having comparable mass area and thickness. Filtration characteristics of prepared filters were determined experimentally in the ultrafine particle size range (20-400 nm). It has been found that the proposed model is able to reasonably predict the measured filtration efficiency, pressure drop and quality factor for all tested filter samples. (C) 2012 Elsevier Ltd. All rights reserved.