The unsteady pulsed-pressure chemical vapour deposition (PP-CVD) technique offers an increase in process intensification over conventional CVD processes due to the high precursor utilisation efficiency. A numerical model of the movement of precursor particles in the process is developed to study the high efficiencies observed experimentally in this process. The modelling procedures were verified via a study of velocity persistence in an equilibrium gas and through direct simulation Monte Carlo (DSMC) modelling of unsteady self-diffusion processes. The results demonstrate that in the PP-CVD process the arrival time for precursor particles at the deposition surface is much less than the reactor pump-down time, resulting in high precursor conversion efficiencies. Higher conversion efficiency was found to correlate with smaller size carrier gas molecules and moderate reactor peak pressure. (c) 2007 Elsevier B.V. All rights reserved.