The task of modeling material heterogeneity (composition variation) is a critical issue in the design and fabrication of heterogeneous objects. Existing methods cannot efficiently model the material heterogeneity, due to the formidable size of the degrees of freedom for the specification of heterogeneous objects. In this research, we provide an intuitive way to model the object heterogeneity by using only a few parameters. These parameters carry physical meanings, such as diffusion coefficients in the diffusion process. We use a B-spline representation to model heterogeneous objects and material properties. We use diffusion equations to generate heterogeneous material composition profile. We then use finite element techniques to solve the material composition equations for the diffusion process. Finally we extend this method to the direct manipulation of material properties in heterogeneous objects.