Previously reported experiments of inertial particle separator (IPS) geometries have focused on standardized sand mixtures that are a particle mixture of various materials, shapes and sizes. These factors make it difficult to understand the effect of particle size and material properties on overall separator efficiency, effects known to be critical to system performance. To address this problem, spherical glass particles with three different nominal diameters were introduced into a two-dimensional wind tunnel configuration representing the critical flow features of an IPS. The facility was used to investigate three different Outer Surface Geometries (OSGs) as well as three different flow splits, i.e. ratios of scavenge mass flow rate to total mass flow rate. The results indicated that large particles with nominal diameters of 120 mu m yielded near 100% efficiency indicating that these particle trajectories are dominated by inertia and wall reflections. As particles became smaller, their separation efficiency decreased, especially at low flow splits. This is attributed to an increased influence of aerodynamic effects associated with particle drag and the OSG. These results were then used to validate a model for determining separation efficiency as a function of particle diameter and flow split. Using this model, experimental and computational data found in the literature are compared, identifying critical particle and flow characteristics for IPS design. (C) 2017 Elsevier B.V. All rights reserved.