Track systems are generally used for large wide windows, where more than the recommended number of panels are required to cover the window. They are ideal for patio or French doors as they give good support to the panels, without the need for a bottom frame. There are two types of track system available:
Bi-fold - the multiple panels on the track can then be bi-folded back to either or both sides at a 90° angle to the track.
Bi-pass - panels can be slid one behind another to either or both sides.