Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for simulating heat transfer in additive manufacturing. Implementations disclosed herein convert a model of an object into a node representation of the object, and generate an adjacency matrix of the object based on the node representation. For each layer of nodes in the node representation, implementations apply a simulated heat to the layer of nodes, and estimating a diffusion of heat to other nodes based on the adjacency matrix. Implementations generate a representation of an estimated heat distribution within the object.