There are certain compatibility requirements for the VFAC boundary condition and VFAC templates. These requirements are discussed in detail in Compatibility Requirements for Model and VFAC Templates, 65. If you plan to change the material properties and make new Patran Thermal radiation resistors without having to recalculate the viewfactors, it is especially important that these compatibility requirements be satisfied for all of the material properties to be used, and that the VFAC boundary condition data do not need to be changed to model the various materials.