Due to the change of standard on the actual manufacturing industry from mass production to a made-toorder perspective, injection mold (IM) manufacturers are often demanded for rapid tooling to deal with small batches and rapid prototyping. The additive manufacturing (AM) process accomplishes such requirements by producing polymer mold inserts quickly while saving costs, regardless of the complexity of the geometry. Despite the appeal of soft tooling, the life of such plastic-made additive IM inserts remains unclear, and numerous studies relate their early failure to non-suitable thermal regulation. Further, the low thermal diffusivity of commercial polymers usually employed on AM IM eventually leads to high cycle times and the uneven cooling of the injected material, affecting the final quality of the part. To cope with such drawbacks, a high-performance polymer conformed by a polycarbonate matrix charged with carbon fibers is formulated in this work to enhance the thermal conductivity of the tooling material. In addition, an accurate optimization methodology based on three-dimensional overset meshes in the finite element method context is introduced to find a suitable arrangement of curved cooling channels (CC) within the insert to improve the temperature uniformity of the injected part. A function involving two terms accounting for temperature standard deviation and maximum thermal gradients on the part is considered for the minimization task. The augmented Lagrangian particle swarm optimizer is employed, and solely the CC subdomain is re-meshed on each objective function evaluation. Numerical simulations are performed on an industrial case which is used to validate the numerical model. The results of this work exhibit not only the reduction of the cycle time achieved by the carbon fiber-charged insert with respect to a non-charged material, but also a marked improvement in the temperature homogeneity of the part obtained by the optimized CC layout. Moreover, good convergence rates of the optimization process are obtained proving that the methodology is suitable to be used in the design of complex IM inserts. Insights of the heat transfer limitations encountered by the composite tool with respect to a steel-made conventional one are given as well.