*** INSIDE REVERSE FOLD ***
Before you can perform a reverse fold, your model must have already been folded enough so that it has two or more layers of paper. A reverse fold is performed on a part of the model that has two layers of paper and is open one side, closed on the other.
With the inside reverse fold you fold toward the open side so that the reverse folded section goes inside the two layers of paper. It is diagrammed using the mountain fold line, a thin arrow indicating the direction of the fold, and a fat arrow indicating that the section to be reverse folded will go between the two layers of paper.