Aluminum lets heat pass through it..... that is why you can pick aluminum foil up straight off the grill and not burn yourself. It is a great thermal conductor, but its small mass and great conductive capacity let it cool off rapidly. It basically passes heat through it. Now the thing in the aluminum foil will retain heat, but not the foil. As for the rack questions i can't help you there as i have never used a rack. But the aluminum tape is just a heat resistant way to tape the heat tape to the cage. I personally place the probes in the viv as that is the area that i want to reach a specific temp, But just on the other side of the glass/pvc from the heat tape.