I would like to smooth green faces together and red faces together on my model (see left part of the screenshot). So, in edit mode, I select the green faces and I apply smooth: "Menu > Face > Shade Smooth". Then, I do the same for the red faces. Problem: the red and green faces are also smooth together. Proof: there is only one edge normal between the green and the red faces. How can I avoid the smooth between the green and the red faces ?