This study developed a numerical model that simulated the degradation rate and temperature profiles of a glass fiber reinforced polyester resin composite exposed to a constant heat flux in a cone calorimeter. By considering the thermal properties of the composite structure consisting of alternating layers of pure polymer and polymer-infused glass fiber mat, the numerical model seeks to reproduce the experimental data from the cone calorimeter test. The final results are achieved through adding a simulated heat flux from the pilot ignition of the degraded gas of the polyester resin. The good agreement between the predicted and experimental results suggests that such models are cost-saving tools over the process of designing and manufacturing of composites for meeting fire safety requirements, without having to fabricate many samples for testing and final selection. Copyright © 2013 John Wiley & Sons, Ltd.