The characteristics of three intumescent fire-retardant materials were examined in a controlled laboratory environment by performing a series of small-scale propane-fired furnace tests. The protective performance of these materials over a selected range of conditions was determined based on the ASTM E119 temperature-time curve for fire tests of building and materials. The objective was to provide a complete set of data needed to validate a new mechanistic model. The latter was developed specifically to predict the thermochemical behavior of intumescent materials when subjected to intensive thermal attack, taking full account of the energy consumption during the intumescent reaction, the temperature range of the tumescent phase, and the effect of thermochemical expansion. Numerical calculations were made to predict the thermal response of the intumescent materials under consideration. Comparisons of the numerical results with the experimental data indicate that the temperature-time history of the substrate temperature can be realistically predicted by choosing an adequate pseudo latent heat for the intumescent reaction over an appropriate range of the tumescent temperatures. The results also indicate that thermochemical expansion plays an important role in the intumescent process.