Viewfactor has been carefully designed to segregate the viewfactor calculations (which depend only on the geometry of the model and are completely independent of the material properties) from that part of the program which creates the Patran Thermal radiation resistors (by combining the viewfactors and material property data). This gives you the luxury of calculating the viewfactors once for a given model. Then if you change materials or material properties, you can get the new Patran Thermal radiation resistors without having to recalculate the viewfactors. The viewfactor calculations typically take a lot of computer time. This capability provides a large saving in computer time for models in which the radiative material properties are modeled for various levels of sophistication or for models in which various materials or surface properties are being evaluated.