Heat Transfer and Reflectivity for Commercial Insulation Panels

[Dr. Angstrom]

Hello, this is kind of a silly question, I guess. I have never done anything with thermodynamics, other than the introductory class in undergrad 100 years ago. I have a practical question. They sell those 4 x 8' insulation panels for homes; .5 - 1" thick poly-isocyanate foam with aluminum reflective layer on one side. What does the aluminum foil layer do? Obviously it reflects light. Does it reflect infrared radiation? I have cut panels to put over my windows at night in the winter and the hottest nights of summer. I have the foil side facing inside the house. Is the foil doing anything for me? Does it still do anything once I close the curtains over it? I was thinking of covering the panels with "Contact Paper" to make them look more appealing. Obviously they would no longer reflect light off the foil layer, but I am thinking that, if the foil is for infrared purposes, the infrared heat radiation would penetrate the Contact Paper(R) and still be reflected by the foil. Or am I totally off the mark here? Maybe the amount of benefit provided by the foil in my application is negligible compared to the basic benefit of the thermal insulation, and I am way overthinking this.
Thank you.

 

[IRstuff]

Does it reflect infrared radiation?

Yes, in addition to reducing the emissivity of the panel on that side

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[3DDave]

Contact paper will convert the IR radiation into heat and warm the foil, similar to covering an optical mirror with contact paper will disrupt the ability to reflect visible light.

 

[Dr. Angstrom]

Thank you 3DDave. So the same as pulling the curtain over it. Which makes me wonder about the efficacy of the foil layer at all, when those panels are used inside the walls of your house as intended, covered up with siding or whatever exterior surface you use.
P.S. OK, I have read up on the use of a "radiant barrier" and the necessity of an air space in front of the radiant barrier. Thank you.

 

[IRstuff]

The radiant barrier is often also the vapor barrier; that said, radiant barriers do need air gaps, so most of the applications shown result in having only the R-value of the foam insulation being effective.

Actually, a curtain would be a better choice, since there would still be an air gap, and the air gap itself provide somes level of insulation, and curtains are often pretty decent thermal barriers on their own, since the weaving and backing often provide some amount of barrier as well.

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[Gholam Baghery]

By removing the foil from the panels, you made them defenseless against vapor, so, they absorbed vapor and in this way, their R-value has been decreased and you have more energy in the room during the summer. It would be the same for the winter and you have less energy in the room during winter. For getting the best result, it would advisable to use a curtain or if you don't want to use a curtain in the room, put the foil outside the window with a small gap by glasses. Obviously, you should solve the wind effect on that foil and keep it stable. In any case, I think it is not a good opinion for removing the foil from the panels.

 

[chicopee]

I do not know about the flammability characteristic of the foam in question but before installing it, get a copy of the manufacturer's spec. sheet to determine if it can be used inside a room without sheet rock or plaster covering. You want to make sure that its flame characteristic is acceptable where you have occupancy. Remember that club in Rhode Island a few years ago. The stage had some sort of foam covering, the type of which I do not know, which caught on fire killing many of the occupants including band members on the stage. Do some research on your foam.
As far as the foil layer on the insulation board, it should face the side exposed to radiant heat but you should maintain an air gap. Now here is one problem that I see and that is if you have glass on a window on which you want that type of insulation. An air gap may not be advisable as you would create a green house effect between the foam insulation and the glass pane exposed to sunlight. In that particular case you may want to disregard the air gap and place the foil backing side of the insulation directly on the glass.