It is recognized that tangible user interfaces (TUIs), defined and scoped by Ishii, provide more intuitive experience for manipulating and reviewing 3D digital information than conventional graphical user interfaces (GUIs). Although current TUIs for CAD enable users to intuitively manipulate and directly perceive 3D digital information via physical objects, they limit users to obtain only external and surface information. The outer 3D physical bounding shape occludes valuable layered and hierarchical internal information. Only when removing and deforming the external 3D physical volumes can users define a section-cut surface to inspect internal information. We propose a TUI system that enables users to visually inspect 3D internal information without modifying its physical outer shell. We implement two popular illustration techniques, namely transparent and cutaway drawings. Using direct touch, hand gestures and tangible tools, users are capable of specifying the transparency and section cut plane intuitively.