Lightweight, high mechanical strength matrix-carbon fibre reinforced composites are manufactured from phenol-formaldehyde matrix/carbon fibre composites by the pyrolysis process. Phenol-formaldehyde matrix/carbon fibre composites are heated in an inert gas environment to high temperatures, for example, up to 800°C in the so-called first carbonization process. Evolution of gaseous species in a relatively thick composite, during the transient heating period, leads to internal pressure build-up, resulting in the composite delamination. The composite delamination depends on the rate of thermal energy flux into the composite material, production of gaseous species via intrinsic chemical kinetics, and transport of the produced gases to the composite environment through its porous structure. A refined transient process model, incorporating the effects of intrinsic chemical kinetics and transport phenomena of heat and mass, still needs to be developed to predict/control the carbonization process to avoid delamination of a composite of thickness greater than 0.001 m. To this end, the overall intrinsic chemical kinetic model being presented here was developed using the experimental data, free of mass and heat transfer effects, on the pyrolysis of a phenol-formaldehyde resin [1]. Insight gained from the thermogravimetric data analyses [2-5] on thermal degradation of polymeric materials was helpful in the chemical kinetic model development.