Midplane is a meshing (finite element modeling) technique that uses 2.5-D (shell) elements to represent a design in 3-D space. This "thin shell" mesh is located at the midpoint of a feature's bounding surfaces and has the appearance of a paper thin 3-D model. The thickness parameter for each element is assigned and is not visually apparent.
As part complexity increases, midplane meshing can become time consuming and may be prone to errors. Therefore, midplane meshing is best completed by an experienced analyst.
Autodesk's Dual Domain or 3-D methods are alternatives to midplane.