A test procedure and method of analysis is presented, whereby the overall decomposition rate of the phenolic binder in a silica-phenolic ablator may be separated into its component reactions. The Arrhenius rate equations for these separate reactions are then determined and a reaction mechanism is postulated which predicts the decomposition rate of the phenolic for both constant and varying test temperatures. To the best of the authors' knowledge, this is the first theory which accurately describes the decomposition rate of phenolic resin, and the method should be applicable to other highly cross-linked polymers.