I was working on a spline path from AI. I extruded it by Extrude nurbs. Then made it editable. Selected the front polygon, then attempted to inner extrude it, but all goes chaotic! 
I tried setting up Quadrangle in regular grid instead of the usual Ngon type. Im using C4D
Manually connect your edges to keep quads, and use something like inset to create a quad border to maintain shape…at least in 3d max terms that’s how you’d do it.
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