An experimental study was carried out to investigate the effects of particles in coating suspensions on the curtain coating window. Different concentrations of poly (methyl methacrylate) (PMMA) particles were dispersed in aqueous glycerol solutions. The maximum coating speed could be extended with the addition of PMMA particles provided the dynamic wetting line was beneath the falling curtain, the so‐called “hydrodynamic assist.” The extension of the maximum coating speed was found to be strongly dependent on the particle number density. The onset of air entrainment was strongly dependent on the ability of direct contact of particles in the suspension with the air film on the moving substrate. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers