An example technique for creating a voxel representation of a three dimensional (3-D) object can include obtaining a shape specification of a 3-D object and a number of 3-D objectives. The example technique for creating a voxel representation of the 3-D object can also include creating a voxel representation of the 3-D object by assigning a material type from a number of material types to each voxel of the voxel representation that defines the 3-D object. The example technique creating a voxel representation of a 3-D object can also include evaluating the voxel representation to determine whether the number of objectives are met.