Reading through your other thread, it would be VERY difficult to accomplish your goal as even if you found a way to completely cover everything with a see through, non-soluble film, you'd then have to deal with trying to cool the components of the system. The CPU, Motherboard, RAM, etc. all need to have a constant airflow around them in order to prevent overheating. If they overheat, they die. By putting a tight fitting substance around the entire board, you would effectively insulate the components which would be very, very bad for their functionality. (Also, it's damned near impossible to find an eletrically non-conductive, yet thermally conductive material. In fact, I don't think a transparent one exists).
So sadly, I do not think there is a substance that would meet your specifications. The only thing I can think of is sealing the motherboard inside of a polycarbonate plastic box with a silicone caulking going around any place that a wire has to enter or exit the system. However, that still wouldn't take care of the thermal problem.