The heart of the pultrusion process is the curing die. After the resin-impregnated reinforcement package leaves the final pre-shaping section, it enters a heated steel die or dies that are in the shape of the finished composite. The dies range in length from 30 to 60 inches and are heated either by electric strip heaters or platens on the top and bottom of the die surfaces. The interior die surfaces are generally chrome plated for increased die life and improved surface finish.

Radio frequency pre-heating is often used in large solid shapes to increase product through-put and give more uniform cure. The RF heating unit is placed prior to the heated die and serves to dielectrically preheat the resin system prior to entering the die. Dielectric heating occurs instantaneously through the resin/reinforcement mass and when, then combined with external die heat, the residence time in the die is reduced and line speed is increased.