Originally Posted by Dave H

In general common cured silicone rubber is non-conductive, a good electrical insulator. For example the good flexible RC wiring has silicone insulation, high voltage powerlines are commonly suspended by silicone insulators, etc.

But be careful, if I remember correctly some RTV (room temperature vulcanization) silicones give off acetic acid while curing, which can corrode copper and solder joints. I think the RTVs sold at auto parts stores marked as sensor safe avoid this issue. Hardware store RTVs, look for electrical connections on the label.