We used sand on at least some of the potting around the sensors for the airbags. Unfortunately I didn't really work on those and don't recall what the purpose was. The potting was a two part but I can't even recall if it was a flexible epoxy or a urethane system. Over 30 years ago now. Unlike these ECUs, the sensors had no transistors, resistors or diodes so sand around them wasn't going to do anything more than fill space and make an insulation.
