Fibrous materials exhibit dramatically different properties than granular materials and packed beds. These differences must be reflected in the choice of a model system. A common prototype model for fibrous materials is packings of ordered or random cylinders (right image). Cylinder aspect ratio can be varied as can spatial correlation and orientational ordering. A different method for creating computer-generated fibrous materials is to use voxel-based techniques. This approach removes the restriction of having straight, rigid fibers (i.e., cylinders), thereby allowing more flexibility in the fiber and pore structures. In either case, the use of computer-simulated materials allows fundamental morphologic parameters to be varied so as to better understand their effects on flow and transport. Important parameters include fiber aspect ratio, solid volume fraction, and orientational effects (which lead to anisotropic behavior).