Denny, the problem with your greenhouse test is you were heating the wrap as well as the metal with the temperature inside the bell - need to do it so the temperatures on each side are different as it would be with a firewall ... fer instance - replace the wood base with pink styrofoam, have the black metal flat against it, have a hole in the foam right under the shiney coated area - or flip the piece so the shiney stuff is up, exposed to the IR, and completely covering the metal and check the temp of the metal vs an uncovered piece
the primary benefit of Protecto Wrap and similar sticky construction materials for us is the prevention of condensation on the inside of the metal panel ... the thermal benefit will not be insulating against conductive heat transfer from the metal panel, but reflection of radiative heating by the shiney side, as in keeping the heat in, not keeping the heat out
Bill
