Aluminum Radiant Foil Insulation

Myron

Does anyone have any experiance with the foil-bubble-foil insulation products? Do they work as advertised/claimed?

I am builing a barn in which I will use PEX tubing in the slab for heating, and at least 4" of fiberglass in the walls and roof, but I am thinking of putting the aluminum foil insulation on the outside of the fiberglass insulation, especially in the roof (instead of using 6" of fiberglass). I am putting up an all steel building, similar to many commercial warehouses, etc, and some mfgs denigrate the radiant foil insulation and say it's a waste of money and others say it is a great product and using fiberglass and foil together provides better overall insulation then just fiberglass.

One problem with these steel buildings is that there is very little insulation value at the purlins and girts because the screws compress the fiberglass to about 1/2" or so. I don't know if the foil will help this or not, considering that it normally requires a minimum 1" airgap to function as designed. Also, does foil lose much of its effectiveness if it gets dusty, or doesn't this matter to the invisible radiant rays?

It costs about $350 more for the radiant foil and 4" insulation as compared to 6" insulation, and I am wondering if this is a good investment, a bad idea or if everyone has a different opinion and no one really knows!

My thoughts are that it should help reflect the radiant rays back into the building during the heating season and during the summer it might keep it somewhat cooler by reflecting the radiant heat from the sun. Anyone have any real life experiances with a similar product?

Mike T., Swampeast MO

REALLY hard to sort the benefits from the hype as related to bubble foil insulation.

They amount to a radiant barrier with some "built-in" insulation (the air). Since the air layer isn't very thick it can't offer much in the way of insulation in the tradiational sense. BUT since it is surrounded by a radiant barrier much of the heat in the form of radiation CAN be blocked making it have an insulative value significantly greater than would be normally assumed.

The "CAN" part of that system is the clincher. To work as claimed the radiant barrier portion of the equation MUST be used.

1) Radiant barriers are generally regarded as "most useful" in warm climates with little requirement for winter heat.

2) Radiant barriers MUST have an air gap on the warm side. An ABSOLUTE minimum of 1" is generally specified--often said to be "better" when > 3" or so.

3) Radiant barriers are considered to have zero effectiveness if covered on both sides. While such can't happen with bubble foil (unless you remove all of the bubbles), the 1" requirement GREATLY exceeds the thickness of bubble foil. If installed with an object against both sides, the insulative value seems reduced to about that of the thickness of the air in the product. I say "about" because it appears that its value is somewhat higher than would be expected, but not much.

4) A covering of dirt/dust DOES affect the performance of a radiant barrier--a significant amount can reduce its effectiveness to near nil.

5) Since radiation arrives and departs a surface at perfectly predictable angles, radiant barriers are generally regarded as most effective when installed flat.

6) A glossy, light colored surface (like a metal roof kept relatively clean and well painted) is itself quite an effective radiant barrier.


Put all of that together and it seems that bubble foil would not be very effective in your application. A insulation product that "sticks" to the structure like icynene would likely be a much better use of your money.

A product that does seem to have promise is radiant barrier (low emissivity) paint. When used outside it helps to block solar radiation from entering the structure. When used as the final interior finish it helps to "trap" radiation from your heating system by "keeping it reflecting" until it hits objects with higher emissivity that you really want to keep warm.

Illustration shows how this works in "perfect" circumstance. The real point is that lowering the emissivity of walls/ceilings/floors in a space DOESN'T REDUCE radiation, it TRANSFERS radiation IN INCREASING ANGLES OF VIEW to objects (like YOU) of higher emissivity. Remember that skin has an emissivity of about 0.98 where 1.0 is "perfect." If EVERY object around your body "appears" to be just the tiniest bit warmer that your skin you will be in essentially perfect comfort--even if the air around you is VERY cold.

Ice has an emissivity of about .98 as well. Think now of a small fire inside of our stereotype of an igloo (domed you know)... Sounds "impossible" doesn't it...

link to one radiant barrier paint product:
http://www.radiancecomfort.com/Products/ab.htm