You can switch the edge dividing two triangle polygons so it connects the opposite corners. This can often make a significant difference in the shape of low-polygon count models or improve the visual flow of a polygon mesh.

For example, the placement or orientation of an edge on a polygonal face could determine the profile and placement of the bridge of a nose or the placement of the cheeks on a character model.

To flip edges

1. Select one or more edges to flip.

   The edge should be a shared edge between two triangles.

2. Select Edit Mesh > Flip Triangle Edge.