I want to place a 1/4 inch thick, 3 inch by 24 inch piece of rigid insulation at the back of each shelf. Then I would glue or tape reflectix to the surface of the rigid insulation. Then I would tape or glue my 3 inch flexwatt to the reflectix.



Are there any issues with glueing or foil taping the flexwatt directly to the reflectix?



There are a couple of issues with this approach. One is that by taping the flexwatt directly to the Reflectix you are allowing the heat to pass through the first layer of foil by conduction. Reflectix and similar products block radiant heat but not conductive heat.



The second is that you'll lose the heat sink effect of the back of the rack.



So you're better off if you attach the flexwatt directly to the inside of the rack and directly to the back. The more direct contact with the back of the rack the better. Then loosely wrap the back of the rack with Reflectix, creating a slight air space between the outside back of the rack and the first layer of foil.



If you want to use the rigid insulation board you're still better off attaching this to the outside back of the rack.

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