Analytical results are presented for the transient ablation performance of a high-performance castable ablation resin for which spallation is responsible for the char removal. The mechanism for the spallation process is assumed to depend upon the internal stress due to the gas pressure drop through the char and a critical char thickness that is related to the surface shear stress. The environmental conditions considered are representative of a ballistic reentry trajectory. Detailed calculations of the temperature, gas pressure, material density, porosity, and stress distribution through the material are presented. The effect of the char porosity on the internal stress is shown. In addition, results that demonstrate the effects of increased heating on the char removal and over-all ablation performance are presented. Nomenclature A = frequency factor Bit B2 = constants in Eq. (7) Cp = specific heat E = activation energy / = porosity HR = heat of degradation k = thermal conductivity K = permeability L = initial thickness m = mass flux M = molecular weight n = order of degradation reaction p = pressure q — heat flux R = universal gas constant t — time T = temperature WP = rate of plastic degradation x = distance normal to surface 5 = char thickness p = density T = gasification ratio (T = normal stress T «= shear stress