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Spray Foam Myth Busters

Spray foam insulation is a very interesting industry.

By Robert Naini

It has expanded from a small niche market that was custom home-builder-centric, and has seemingly exploded to over a billion-dollar industry in a relatively short 15 years or so.

Now, don’t get me wrong, spray foam has been around for more than 15 years, but in the past 15 years it has moved from being focused on the custom residential industry to include a variety of applications:

  • Residential Retrofits,
  • Production Builders,
  • Light Commercial,
  • Large Commercial,
  • Industrial, and more.

With this meteoric rise and the success of spray foam insulation, there seems to be a never-ending list of market assumptions, developments in the building code, and design questions. Some of the questions are relevant and important, while others are obviously founded in ignorance.

Let’s take a look at five myths that loom over the spray foam industry and offer some clarification.

Imagine you are working your own booth at the local homebuilders show.

You are in a 10? x 10? booth space. You’ve got a display that compares open-cell, closed-cell, and fiberglass. It’s got light bulbs that create heat in the bottom compartment and a fan that pressurizes this compartment to show booth visitors that air passes through the fiberglass, but not through the open-cell and closed-cell foam. You’ve got pictures on display, a flipbook of projects that you have completed, and a TV showing a loop video with lots of rising foam to catch the attention of attendees.

Can you picture it? You’ve been there before right?

The first person of the day walks by, the video of the rising foam catches their attention and they say, “WOW, that’s cool. What is this stuff? I’ve never seen it; it must be new.”


While manufacturers are constantly developing new formulations, to offer the market more competitive, higher quality products, spray foam insulation is not new.

Actually, modern SPF dates back to the 1930s, when a German scientist, Dr. Otto Bayer, discovered and received a patent for the fundamental chemical reaction that is the foundation for polyurethane. In the 1960s, polyurethane foam was commercially available and could be found in appliances, furniture ,and automobiles.

All we have done is taken what was traditionally an in-plant application and moved all of the equipment into a spray foam rig so we can roll out to a jobsite and create an insulated “cooler” out of your building.

Soon thereafter, another attendee, looking at the side-by-side comparison box, asks, “Closed-cell foam is better than open-cell foam, right?”


It’s not as simple as one being better than the other. Closed-cell foam is the better choice in some applications and open-cell foam is the better choice in other applications.

Remember, open-cell foam has limitations:

  • It’s not intended for exterior applications.
  • It’s not intended to be used in below-grade applications.
  • It’s not designed for contact with bulk water.
  • And, it’s not a Type II vapor retarder.

Closed-cell foam is more versatile than open-cell foam, so if any of these are design parameters, then yes, closed-cell foam is not only a better choice, it is the only choice. This means that exterior building envelopes, below-grade basements, wine rooms, pool houses, and other applications with significant temperature and relative humidity differences, are all obvious closed-cell foam applications.

On the other hand, when used appropriately, open-cell foam wins the economic analysis every time. Both types of foam are air barriers and when installed at equivalent R-values (i.e. different thicknesses), closed-cell foam can easily cost twice as much as open-cell foam, because the cost per R of closed-cell foam is double that of open-cell foam, with no thermal performance difference.

So, because open-cell foam is more cost-effective when installed at equivalent R-values, its payback timeframe is much quicker. This means open-cell foam is typically the better choice for interior applications that don’t require the additional physical properties of closed-cell foam; most often this includes interior building envelope applications, like wall cavities and attics, in climate zones 1 through 4.


Next, an attendee comes by and says, “The guys in the booth over there said 3? of their closed cell foam has ‘effective R-value’ of R-38, what’s the effective R-value of your spray foam?”


No, this is not correct.

Your spray foam insulation does not have a higher “effective R-value” than its tested R-value. Stop saying that it does – this is illegal, and gives you and the industry a bad reputation.

R-value is R-value; it is derived and documented based on a tested value, K-Factor, and does not magically have a higher resistance than the value listed on its TDS just because you think it is better.

Let me explain.

K-Factor is a physical property measured using ASTM C-518 and is important when it comes to optimizing a building’s thermal performance and meeting energy code. K-Factor is a material’s thermal conductivity; measured as the amount of heat that passes through a thickness of material per unit area in one hour, if the temperature difference between the hot and cold side of the material is one degree. So the lower the K-Factor, the better the thermal performance. To put units to it, it is the number of BTUs that would pass through one inch of a spray foam material per square foot, in one hour, if there was a one-degree Fahrenheit difference between the hot side and the cold side of the foam sample.

While K-Factor is the measured value, most of the construction industry works with and refers to R-value.

R-value is thermal resistance and is the inverse, or opposite, of thermal conductivity (K-factor), so the higher the R-value, the better the thermal performance. R-value is the amount of heat that is resisted and does NOT pass through a thickness of material per unit area in one hour, if the temperature difference between the hot and cold side of the material is one degree.

When it comes to the building industry and all of this thermal performance business, the problem is that K-Factor and R-value only measure one form of thermal transmission, conduction, or heat transfer by touch; these values do not address convection (heat transfer by air movement) or radiation (heat waves).

So, R-value alone does not tell the whole story.

R-value of an insulation can be derated, based on poor application, this is where effective R-value comes into play. All insulations are designed to be installed so that they are in contact with an air barrier on all six sides of the insulation. So, if fiberglass or cellulose is not installed properly, not uniform and has gaps and voids, it can be derated. Meaning its effective R-value would only be a fraction of its tested value.

This is a little different for spray foam insulation, because the insulation is an air barrier. In a stud-wall cavity application, the insulation does not have to contact the inner face of the cavity, because the insulation is already on the same plane as, and is already in contact with, the air barrier because the insulation and the air barrier are the same material.

By providing an air barrier solution, spray foam can reduce a structure’s convection heat transfer load and provide a thermal benefit that is not captured by R-value.

Additionally, spray foam insulation can also have an impact on radiant heat transfer and the associated radiant loads.


Have you wondered why a traditional, vented attic temperature could easily be over 120°F when it is only 90°F outside? This is primarily due to heat radiating off of the superheated roof deck to the inside of the attic.

Under the hot sun, a black shingle roof could easily exceed 150°F surface temperature and as the heat conducts through the roof deck, the interior roof deck surface might be close to 140°F. This heated surface acts like the heating element in your toaster and radiates heat into the attic heating the air up to 120°F.

By installing spray foam insulation to the underside of the roof deck, just like turning off your toaster, you change the temperature of the interior radiant surface. The new radiant surface is the exposed surface of the spray foam and rather than being 140°F, like the exposed roof deck, it will be closer to the interior conditioned temperature, around 80 to 90°F, thus having a tremendous effect on radiant heat transfer.

Overall spray polyurethane foam can address all three forms of heat transfer:

  1. Conduction, of course, with its tested and documented K-Factor and R-value;
  2. Convection because of its air barrier qualities;
  3. And, radiation because the temperature of the exposed radiating surface is significantly lowered.

This is why spray foam outperforms other insulation materials, not because of some magic “effective R-value,” but because spray foam can fundamentally and scientifically have an impact on all three forms of heat transfer.

Immediately after that, another attendee says, “But if spray foam works so well, can’t you make the house too tight? I mean, doesn’t the house need to breathe?”


No, your house does not need to breathe. It does not have lungs. The people in the house are the ones that need to breathe.

Even if houses needed to breathe, that’s not a very good justification to build leaky, drafty, inefficient buildings.

For energy efficiency and interior comfort purposes, the best approach is to seal the structure as tight as possible, then take care of the indoor air from the inside out, with a proper air management system. After sizing the mechanical system, there are several options for providing fresh air ventilation that range from a simple damper controlled inlet duct that is installed on the return side of the HVAC system, all the way to the high-end energy recovery ventilator, which will condition the supplied air using energy from the exhaust air.

The best building science has to offer is, “Build it tight and ventilate right.”

Finally, right before lunch, you get the granddaddy of them all, possibly the biggest, most misunderstood idea when it comes to spray foam insulation, “I love foam, but this stuff is too expensive.”


WOW, this is a shortsighted point of view.

Yes, when installed , spray foam is going to cost more than traditional insulation upfront.

Guess what, a high-performance machine always does!

But the standard payback period, for both open-cell and closed-cell foam, in all climate zones, is less than five years. That’s more than a 20 percent ROI.

Where else are you making 20 percent on your money?

Also, even if the spray foam upgrade costs an additional $10,000, when financed over 30 years, that adds less than $50 to the monthly payment, and with a typical energy savings that can be $100, $200, or more per month, the homeowner is in positive cash flow from day one.

Finally, for you cash buyers that don’t care about payback, ROI, or positive cash flow compared to financing costs, when mechanical systems are properly sized and designed, based on the building envelope package, using spray foam insulation can reduce the size of the mechanical system, which means the mechanical system may cost less upfront.

With these concepts in mind, traditional insulation will cost you more in the long run, so if you ask me, it is too expensive not to use spray foam.

The point is that spray foam is the only upgrade that will not only pay for itself, but it can also buy granite counter tops.

Is this possible? While working a simple tradeshow you get questions about five spray foam myths, all before lunch.
It has happened to me; it can happen to you. •

Robert Naini has a Bachelor’s of Science in Mechanical Engineering and an MBA from the University of Texas at Arlington. With more than 12 years of experience on the cutting edge of spray foam insulation, he has developed a unique knowledge base including sales & marketing, employee & applicator training,building science awareness and building code expertise. Leveraging his spray foam knowledge and business know-how, Robert has helped both manufacturers and contractors grow their businesses. Spray Foam Advisor offers videos, blogs, and more to help you GROW Yourself, GROW your Business, and GROW the Industry. Create a free account today at