Abstract Previously we investigated the effect of porosity on solid-particle erosion of metal–matrix composites (MMCs) using a dynamic wear simulation model and demonstrated a positive effect of porosity on the resistance of MMCs to erosion when the amount of pores was small. We have extended this work to other materials, including pure metal, ceramic, and ceramic–matrix composites (CMCs), in order to obtain a general view of the role that porosity plays in solid-particle erosion processes for a wider range of materials. In this work, we simulate the performance of Cu, TiC–Cu, AlMgB 14 , TiB 2 , and AlMgB 14 –TiB 2 , which contain different amounts of porosity. It is demonstrated that a small amount of porosity has a positive effect on the erosion resistance of the metal but the beneficial effects diminish as the reinforcing phase is added. It appears that pores play a dual role: providing preferential sites for crack nucleation but forcing cracks to zigzag with elevated energy dissipation. Thus, a beneficial effect of porosity exists as long as the dual role is in an appropriate balance. However, porosity is always detrimental to ceramic materials, which are hard and brittle, susceptible to defects with low capability to absorb deformation energy, since the crack propagation in brittle materials only needs a small amount of input energy to generate fracture surfaces with little associated plastic deformation.