Under-slab Bubble Foil Insulation: Reflective Insulation

Radiant Heating Design Guide
radiant floor heat

Mislead by Marketing...

The performance of radiant barriers in wall and roof assemblies can not be contracted with underslab applications. 

If a distributor or manufacturer intentionally or unintentionally has lead you or anyone you know to this conclusion, contact the Federal Trade Commission

toll-free #:

The heat transfer problem to solve with a slab on grade is conductive not radiative - unless of course one deliberately creates a radiative problem to solve so one can sell reflective materials...need a moment to think about that...go ahead and take your time.

Sand as an insulator

Here's the scoop on sand as an insulator...dry sand has an approximate  thermal conductivity of 0.17 Btu/hr ft deg F which means it is a very poor conductor and a  reasonable insulator - here's the caveat - so long as it remains dry.

Wet sand (over 20% moisture content is very good as a conductor having a nominal thermal conductivity of 1.25 Btu/hr ft deg F which makes it a lousy insulator.

Mother Nature has a punishing way of dealing with those who think they have the magic powers to prevent changes in moisture content...just something for you to think about before listening to the snake oil foil story...


Ambiguous Information

One common element to non rigid insulation sold for underslab application is ambiguous information used in the sales pitch. Ambiguous means:

  • of doubtful or uncertain nature; difficult to comprehend, distinguish, or classify.

  • lacking clearness or definiteness; obscure; indistinct: an ambiguous shape; an ambiguous future.

Here are five more examples of ambiguous information from manufacturers with these claims, “The Industry's #1 Selling Under-Slab Insulation!", or, "The Industry's Premier Under-Slab Insulation".

Example #1) on their website they show an illustration of a reflective radiant image BUT don’t actually claim that the product reflects heat back into the underside of the slab…however the phrase “…effectively control all three modes of heat transfer -- Conduction, Convection and Radiation.” in conjunction with the image could imply to the unsuspecting consumer that radiant transfer occurs - without actually making the claim - ambiguous…tsk tsk.

Example #2) They make a comparison between their tarp type product and foam wherein the tarp reflects radiant heat transfer and the 2” Foam board absorbs radiant heat transfer. So here's the thing - there is no airspace between the slab and product ergo there is no radiant transfer - ergo the statement is false. The foam board doesn’t absorb radiant energy it slows down conductive heat transfer just as the tarp does.  Incidentally some manufactures have multi layers of air bubbles with a reflective barrier in-between - in other words they create the problem so they can solve it with their products...remember when you're grandma used to say, "you never ask a barber if you need a haircut"...well the same applies to sales people selling reflective foils for under slabs.  This is the same reason why some States have now legislated indoor air quality investigators who identify IAQ problems can no longer be the solution provider on the project...now why do you think they would make such laws?.

Example #3) In a comparison test they make the claim that their product is  61.9% warmer when in fact its only 1.72 deg F warmer than the foam board which is not 61.9%. It gets better - the surface temperatures shown are grossly over the safe comfort levels - in fact the heat should have been removed before it hit 84 deg F - the recommended maximum for comfort - had they done that the results would have shown zero difference.

Example #4) They provide test results showing an R-value of 7.54 but what consumers need to know that value includes the 4" concrete,  2” gravel and 1” of sand - it does not represent the ” thickness of the actual product.

Example #5) The site effectively uses, marketing masquerading as science, when it implies that foam will stabilize at soil temperatures and then become a consistent drain on the radiant system and the slab. It goes onto to state that it’s product is more effective and efficient. The facts: No insulation provides "a consistent drain", all underslab insulation does is slow down conductive heat transfer and brand x is no more special than any other product. Furthermore, unlike foam, aluminum is an excellent conductor and is the last thing one would wants to use as a conductive barrier. 

According to the Wisconsin Department of Commerce evaluation, this product can be installed but no credit will be given as under-slab insulation. They go further by stating (brand x), "SHALL NOT BE INSTALLED AS A STAND ALONE PRODUCT IN LIEU OF THE CURRENT CODE REQUIREMENTS."

Given the choice between trusting the sales and marketing pitch from The Industry's #1 Selling Under-Slab Insulation!", or, "The Industry's Premier Under-Slab Insulation" or the Wisconsin Department of Commerce, Safety and Building Division - we're going with the Safety and Building Division...just in case anyone was wondering.


June 2010 Update:

We found another online reseller providing ambiguous information.

This company is sharper than the average flogger of foil, here's their approach:

They start out with the product description of, " 48" x 125' Concrete Under Slab Insulation " and follow with this statement, "Insulating where there is contact with the ground is always tough on insulation. The ground is an infinite heat sink and will constantly pull heat from your living space. Traditional insulation like fiberglass is largely ineffective in below ground applications. The higher the moisture, the worse fiberglass performs." Ok so the unsuspecting consumer reads that this bubble foil product is for concrete under slab insulation and confidence is built up with a series of true statements - except we know of no building codes which allow fiberglass insulation as under slab insulation. If anyone can provide information to the contrary we'll be happy to retract our statement.

Then they go to this ambiguous statement, " brand x is a white / double bubble / foil reflective under slab insulation product...The design of the product makes it ideal for use in radiant heat floor systems, wrapping foundation walls, and many other concrete insulation projects. Not only is brand x, a radiant barrier, but it's also a vapor barrier giving you two products in one." So here's the thing, brand x used a very good editor and in our opinion, arranged the words in such a way to avoid being targeted by the FTC lawyers - but come on folks, in our opinion, using 'concrete under slab insulation' and 'radiant barrier' in the same sales pitch obfuscates the reality that concrete on ground looses heat by conduction not radiation. 

Message to consumers: When manufacturers create a radiant problem when none existed, so they can solve it with their radiant barrier products you might want to think twice about your choice.

Federal Trade Commissions toll-free #: 1-877-(382-4357) (...operators are standing by).


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