A model is developed to describe flow in porous media from the thermal decomposition of binder in three-dimensional bodies with anisotropic permeability. The model is able to describe the pressure within the body as a function of position, time, and temperature during the heating cycle. The results from numerical solution of the un-steady-state partial differential equation are compared to those obtained from an analytical solution to the steady-state equation. Under many conditions that are representative of binder removal, the analytical solution provides a reasonable representation of the numerical solution. A criterion is also developed to determine when the analytical solution is valid. Scaling relationships for the buildup of pressure in terms of the dimensions of the body, the rate of reaction, and the permeability are also derived.