In a computational modeling method for identifying how to apply a modifying agent during a three-dimensional (3D) printing method, a thermal diffusion model of a layer of a 3D object to be formed from a portion of a sinterable material using the 3D printing method is created. The thermal diffusion model is created by a computer running computer readable instructions stored on a non-transitory, tangible computer readable storage medium. A quantity of the modifying agent to be selectively applied is calculated, by the computer, based upon the thermal diffusion model.