How to inset near a mesh boundary without creating new border faces? I was following a tutorial to create a helmet.
A the step for the mesh under the cube he insets a face to create an indent, but only insets the side of the mesh, not the open border.
How did he do it?
You can do this using the 'Inset' tool.

Select the faces you want to inset:



Press I to trigger the 'Inset' tool and move the mouse to increase or decrease the amount. Press B during the inset to turn on the 'Boundary' option (which will stop creating faces along the boundary of the mesh): 



Press Enter when you are happy with the inset and then delete the inset faces with X> Faces