Chris_launder, I have always used Rightway Audio Isolators, which are no longer available. They are ceramic with a brown glaze and look much like what you used to see on low voltage power lines. One can rest cables in the groove. I have tried cardboard, wood of different types, and the special and anti-static foam in which chips are shipped, and other ceramics, but none have been the equal of the Rightways.
You can see the contraption I use under the HFC UR speaker cables in my review of these cables on StereoTimes.
You can see the contraption I use under the HFC UR speaker cables in my review of these cables on StereoTimes.