Temperature and conversion profiles during hot curing of an unsaturated polyester resin were studied. It was found, unexpectedly, that the reaction exotherm was largest in the outer layer close to the hot mold surface and least in the center core. The opposite was true for room temperature curing with a different initiator system. Comparison of the experimental results with heat transfer calculations has led to the conclusion that the kinetic character of cure across the polyester slab thickness was location-dependent. The variation with location was interpreted in terms of diffusion of the initiator components from the core towards the surface owing to their faster depletion close to the hot surface and the imposition of a temperature profile. Simulation of the experimental results was possible by combining the heat transfer equation with a kinetic equation accounting for an inhibitor induction time and a modified Arrhenius equation containing a location-dependent activation energy.