I see you edited in the part about the noctua. But even then you’re wrong, you don’t need to worry about the sides insulating. As long as you have your intake and outtake fans properly oriented and running at sufficient speeds to move air through you can cover the side panels without concern.

In fact if your side panels have holes sealing them will improve performance by smoothing out the airflow, since reduced turbulence means air spends less time in the case before going out