The Transparency subnode () adds transparency to 3D plots. Add it to make the plot more or less transparent. Contour, Image, Isosurface, Layered Material Link, Line, Mesh, Multislice, Radiation Pattern, Slice, Streamline, Surface, Surface Slit, Table Annotation, Volume, Waterfall, and Whirl plots in 3D support the Transparency attribute. In the Model Builder, add one of those plot types; then right-click the plot node and select Transparency.

In the Transparency field, or using the slider underneath, specify the transparency as a value between 0 (no transparency) and 1 (fully transparent).