The front- and cab-design is the most significant feature of the IC3 (and its cousins). When viewed from the outside, the viewer will notice the large rubber diaphragm surrounding a flat cab. The cab is separate department in the train, but the table with the controls are mounted on a huge door, to which the seat is also mounted. When two or more units are coupled together in a single train, the entire front door folds away to give a wide passage, and the rubber diaphragms at the ends form a flush aerodynamic seal. The IC3 can also couple and run in tandem with the electrical version, the IR4. Up to five trainsets can be coupled together. In case of shuttle reason the IC3 can also be coupled mechanically with its Flexliner little sister IC2 but not the cousin ET-FT-ET.