Cut bumper holes for radars in hyperion kit

The hyperion kit recommends cutting holes in the bumper to expose the radar units. I imagine this step is necessary for the performance of the radar and not just to make the radars more easily accessible, correct? Is there any material that we could put over the holes that would not degrade the performance of the radars?

The holes in the bumpers are for performance reasons, to avoid any distortion of the RADAR EM signal. It is recommended to keep the RADAR uncovered for the best performance.