The flattening of aluminum and copper particles cold sprayed onto ceramic surfaces has been described by an ellipsoidal function. The accuracy of this approximation was verified from particle dissections performed in a focused ion beam/scanning electron microscope (FIB/SEM). Flattening data were collected from SEM measurements. It was shown that aluminum particle deformation was limited below similar to 5 mu m, and copper deformation below similar to 2 mu m. Deceleration of the particles through the bow shock, strain rate hardening and thermal conduction were factors that contributed to the differences in deformation behaviour. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.