The Surface-to-Surface Radiation (rad) interface (), found under the Heat Transfer>Radiation branch (), is used to model heat transfer by radiation. It treats thermal radiation as an energy transfer between boundaries and external heat sources where the medium does not participate in the radiation (transparent medium).

From the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Surface-to-Surface Radiation to select physics features from the context menu. For the Surface-to-Surface Radiation interface, select a Stationary or Time Dependent study as a preset study type. The surface-to-surface radiation is always stationary (that is, the radiation time scale is assumed to be shorter than any other time scale), but the physics interface is compatible with all standard study types.