PDP-8 case

I've been cleaning up my recently-acquired PDP-8/E, and I've had to remove the plastic foam from the inside of the lid, which was fairly horrible. I'm not sure what best to replace it with, as the foam was in two parts. The square(ish) area above the rear Omnibus section was ordinary brown high-density plastic foam, about 3/8" thick, but most of the area above the front section was black conductive foam. Is this original? Was it supposed to protect the boards that have H851 over-the-top connectors from static that might have been carried by ordinary foam? I'd have thought the leakage through the conductive foam might upset some circuits. So, should I use ordinary high-density foam, or conductive? -- Pete Peter Turnbull Network Manager University of York