Many models have been published to predict frost growth. These may be divided into empirical and theoretical models. All prior theoretical models assume the water vapor is saturated at the interface between the air stream and frost layer. This paper provides a new theoretically based numerical model of frost deposition and growth. The present model: (1) uses supersaturated water vapor at the frost surface, which is fundamentally correct; (2) improved correlations for frost thermal conductivity; (3) uses a rationally based tortuosity factor; and (4) calculates the local frost density variation. For numerical simulation of the frost growth rate, the, measured thermal conductivity was used. Frost growth rate on a cold surface was measured, and the experimental data were compared to the numerical model and agreed within 15%. The proposed supersaturation model was also compared to previous investigators' experimental data, and it was found that the supersaturation model is superior to analytical or numerical models that assume the water vapor at the frost surface to be saturated. (C) 2003 Elsevier Ltd. All rights reserved.