Methods and systems for modeling a porous physical object for layered manufacturing are provided. A model of an object includes geometric and material porosity models, each of which are divided into two-dimensional layer representations. Each two-dimensional layer represents a cross-section of the geometric model and material porosity model of the object, respectfully. The material porosity layer representations specify a material porosity variation for the layer. Geometric and material porosity contours of the model are created by iso-Z surface extraction for each layer. Using the contours, a boundary constrained line representation of each two-dimensional layer representation is generated using continuous space-filling fractal curves to characterize the material porosity variation for each two-dimensional layer.