A theoretical model is proposed for curing thermosetting polymers. The following heat transfer mechanisms are taken into account : convection through the heated fluid-mold interface, conduction through the resin, and heat generated by chemical reaction. To study the influence of the convective heat in the curing step of the polymers, different external heating fluids are considered. Several chemical systems are used in the simulation. The results show that an epoxy requires precise control of thermal runaway. Criteria for processability are established and they provide a cycle time without promoting a damaging exotherm.