Quantitative and visual data on defrost are presented. The data base comprises normal and in plane images of the defrost process over a range of ambient temperature, dew point, and surface temperature. Twelve frost layers are created at prescribed surface temperature, dew point, and ambient temperature. Melting is initiated by application of heating on the frosted surface. Predictions of the multistage defrost model developed in Chap. 3 are compared to the reduced data where possible, and empirically based relations for heat and mass transfer are developed. Assumptions used to simplify the differential equations for coupled heat and mass transfer in Chap. 3 are validated by the measurements. Overall defrost efficiency is proportional to initial frost thickness.