The process to be modeled produces micro-hollow particles based on spray drying technology. This process involves droplet formation, solvent evaporation, formation of the impermeable outer layer, and decomposition of a blowing agent. The objective of this work is to develop a fundamental model that describes the formation of the hollow particles starting from a single droplet. This model is then used to predict the time to skin formation and total drying time. The effect of parameter uncertainties and varying operating conditions are investigated. (c) 2005 Elsevier Ltd. All rights reserved.