The Radiation in Absorbing-Scattering Media (rasm) interface (), found under the Heat Transfer>Radiation branch (), is used to model radiative heat transfer inside participating (semitransparent media) media supposed to be nonemitting.

When the physics interface is added, these default nodes are added to the Model Builder: Absorbing-Scattering Medium and Opaque Surface. In addition, when Discrete ordinates method is selected, Continuity on Interior Boundary is also added. Right-click the main node to add boundary conditions or other features. Then, from the Physics toolbar, add other nodes that implement, for example, boundary conditions. You can also right-click Radiation in Absorbing-Scattering Media node to select physics features from the context menu.