In lost foam casting of aluminum the liquid metal normally decomposes the foam pattern by ablation. But sometimes polymer vapor bubbling through the liquid metal accumulates along an upward-facing flow front until it opens a finite gap between the liquid metal and the decomposing foam. This changes the foam decomposition mechanism along that front from direct ablation to melting. A mathematical model is formulated for heat conduction, convection, and radiation across the gap, coupled with the vaporization of the excess polymer liquid behind the metal front and the resulting buoyant movement of polymer vapor bubbles through the liquid metal. Both models are combined to obtain an analytical solution for one-dimensional bottom filling of a pattern with uniform thickness. The results from this solution not only compare well with available experimental data, but they also explain how part thickness, metal temperature, and pressure affect filling speeds in bottom-fill situations. (c) 2006 Elsevier Ltd. All rights reserved.