According to examples, an apparatus may include a processor and a memory on which are stored machine-readable instructions that when executed by the processor, may cause the processor access a thermal simulation of a three-dimensional (3D) model, the thermal simulation identifying thermal values simulated to occur across the 3D model during fabrication of a 3D part corresponding to the 3D model. The instructions may also cause the processor to determine a modification to be applied to first thermal values corresponding to a first section of the 3D model, in which the modification may increase accuracy of the first thermal values in the thermal simulation and to apply the determined modification to the first thermal values to generate a modified thermal simulation of the 3D model.