The Prescribed Density Boundary feature () can be added from the model tree under Component using the Topology Optimization context menu. It acts on boundaries of Density Model features, which use Helmholtz filtering. The feature constrains the filtered field to 0, 1, or θfix on its selection.

From the Fixed value list, choose User-defined, Void, or Material. The Void and Material options corresponds to the Prescribed Void Boundary and Prescribed Material Boundary features, respectively, while the User-defined option allows setting an arbitrary value, θfix, to be used for the constraint.