The effect of fiber alignment on particle collection performance of mechanical/electret filters are investigated numerically. Four sets of fiber networks, namely, nearly isotropic, aligned, highly aligned and layered orientations are constructed using Voronoi tessellations. The particle transport and deposition process in these fiber networks under the coupling of flow field and electrostatic field are modeled using hybrid lattice Boltzmann Lagrangian method. The particle collection efficiencies and pressure drops of the mechanical/electret filters are calculated and compared. Results indicate that the mechanical filter with layered networks has the best filtration performance for large particles, and then the aligned networks has the next best performance. However, the sequence reverses when filtering the nanoparticles. In contrast to a mechanical filter, the electret filter with isotropic networks exhibits the best performance for full range of particles size, indicating that the dielectric attraction is less impacted by the 3D fiber orientations. Increasing fibers orientations in the airflow direction and constructing 3D pores of high sphericity are recommended to improve the performance of an electret filter. (C) 2018 Elsevier Ltd. All rights reserved.