Spray Foam Insulation compared to Blown Fiberglass (Performance Test)

Oak Ridge National Laboratories did some testing to show how fiberglass insulation compares to spray foam insulation in attics for both cold and hot conditions. Evidence shows that spray foam insulation in "real world" conditions outperforms fiberglass even when it is installed with a much lower R-Value. The evidence clearly demonstrates that insulation R-Value does not account for all of the energy efficiency characteristics of sprayed foam insulation.

Attic Spray Foam Installation Example

Below: a professional SPF applicator installs closed cell spray foam insulation in an attic:

Spray Foam Insulation must be applied on a clean dry surface. No fasteners are required because SPF foam is self adhering (aka self flashing). The foam cures within about 1 minute to near full hardness, and creates a seamless monolithic barrier, which is superior for prevention of moisture and vapor transfer. Conventional insulation quality benchmarks (such as R-value) greatly under-represent the quality and effectiveness of sprayed foam, which is by far the best insulation on the market. Many professional contractors estimate that just one inch of SPF closed cell foam is as effective as four inches of fiberglass!

What is R-Value & Why Does It Matter?

R-Value is really just one way of measuring the quality of any given type of insulation. For example, if an insulation product was rated at an R-Value of one, this means, 1 inch of the product would be equivalent to about 1 inch of wood. Here's a more formal definition:

R-Value: A form of measurement which expresses a level of thermal heat resistance. “R” is the measure of a substance’s resistance to heat flow. An “R” value is a number assigned to insulation; the higher the number, the better the insulation. U-Value, explained below is the reciprocal of R-Value (flip the numerator & denominator of number to get each corresponding value).

U-Value: The opposite of R-Value. The overall coefficient of heat transfer of an assembly measured in BTUs per square foot, per degrees Fahrenheit difference in temperature per hour.

In short, R-Value is way to benchmark the effectiveness of an insulator. However, unfortunately, the measurement is not effective because factors such as moisture trapping and vapor movement are not considered. For example, a seamless monolithic barrier of Foam will effectively trap moisture and block vapor transfer, while standard fiberglass is not nearly as effective. In other words, just looking at the R-Value of closed cell foam greatly underestimates the effectiveness of spray foam insulation. Sprayed Polyurethane Foam (SPF) is the same material which is used in our everyday refrigerators. This is because it provides superior insulation--trying to line a refrigerator with fiberglass instead (for example) would be just plain ridiculous. Unfortunately, poorly written insulation regulations and laws have actually (at times) prevented contractors from using SPF foam (a superior product) in attics in colder climes!

One-Dimensional Legislation Requires High R-Value; Ignores Performance

Some poorly written insulation requirements, usually in cold climate ares, actually prevented contractors from installing sprayed foam insulation in places like Wisconsin where an R-Value of 49 were prescribed for attics. This unfortunate, unfair, and outdated legislation prevented spray foam insulation from being installed in new homes. Instead of requiring the insulation to maintain specific temperatures, or perform in a specific way, this arbitrary legislation was based on a benchmark (R-Value) which is now outdated. People with spray foam insulation and contractors alike were aware of the superior qualities of closed cell foam for many years, but were unable to act on that knowledge. Hard evidence would be required into order to push through some legislative changes.

An example of a Pink Blown Fiberglass Installation:

Spray Foam Insulation vs Fiberglass: The Laboratory Test

In order to dispel the R-Value myth once and for all, the Spray Polyurethane Foam Alliance (SPFA) commissioned Oak Ridge National Laboratories to perform a large scale attic simulation (in 2005). The test would entail collection of data and performance evaluation of various types of insulation in 'real life' scenrious and then benchmark the results vs R-Values (to show how accurate, or innacurate R-value is for predicting insulation performance.

SPF Foam vs Fiberglass: Testing Area & Conditions:

Summer and winter conditions were simulated for three types of insulation in an 8x8 thermal test area of 64sq feet. Both low density and medium density polyurethane Sprayed Foam Insulation of 4" to 5.5" was compared to typical blown-in Fiberglass insulation of 14". Here's a summary of the three types of insulation which were tested in the thermal attic simulation:
1-Fiberglass: Fourteen Inches of Loose-Fill fiberglass on an attic floor
2-Sprayed Foam Insulation: (Low Density) Five and 1/2 inches of low-density polyurethane foam between rafters and the underside of the roof deck
3-Sprayed Foam Insulation: (Medium Density) Four inches of 2lb medium-density polyurethane foam between rafters and the underside of the roof deck

SPF Foam vs Fiberglass: Test Results:

So here it is, the moment of truth. Just how did 4" to 5.5" of spray foam insulation measure up vs 14" of fiberglass? Keep in mind that 14" of fiberglass contains substantially more R-value than a mere 4" of low density foam.

The results shakedown:
Blown Fiberglass Assembly 14":
46% R-Value maintained at cold outside temperatures (7°F avg surface temperature)
51% R-Value maintained at hot outside temperatures (107°F avg surface temperature)

Low Density Foam Assembly 5.5":
74% R-Value maintained at cold outside temperatures (61°F avg surface temperature)
61% R-Value maintained at hot outside temperatures (78°F avg surface temperature)

Medium Density Foam Assembly 4":
83% R-Value maintained at cold outside temperatures (60°F avg surface temperature)
67% R-Value maintained at hot outside temperatures (77°F avg surface temperature)

Notice the huge temperature range of the fiberglass during cold or heat, while the foam maintains a very small range of interior temperatures. The fiberglass got extremely hot in the heat, and the fiberglass also got extremely cold during the cold. Now, take note of the % R-Value maintained. This means that in extreme conditions, the actual fiberglass performance was only 51% of the stated R-Value in high heat, down to only 46% of the R-value in cold weather! Now compare this to medium density foam, which performed at 83% of the R-Value in heat, and 67% of the R-Value in cold.

in extreme weather conditions SPF foam outperforms fiberglass 40-50% in terms of R-value retention. So, as an example, an estimated R-Value 10 of foam (medium density) can perform as well as an R-Value 17-20 of fiberglass, during extreme weather conditions. Hence, in an area like Wisconsin, where a minimum R-Value 49 was required, foam thickness reaching an R-value of 34 (5.5" of low density foam) would outperform a thickness of blown fiberglass with R-Value 49 (16" of blown fiberglass).

SPF Foam vs Fiberglass: Results Analysis

In other words, Foam requires less R-Value to provide the same benefit. Based on the chart below, 14 inches of fiberglass provides a raw R-Value of about 42, while during an actual test, it only performed at 46-51% of that (i.e. under extreme weather, the fiberglass had a true R-Value of 19-21). While the low density foam represented an R-value of about 34 (6.25 per inch, with 5.5 inches), and maintained most of that during even the most extreme conditions (i.e. under extreme weather the true R-value of the foam was 21-25). The medium density foam outperformed the fiberglass by an even larger margin. The takeaway here is clear. A lesser amount of R-Value in foam outperforms a much higher R-value in fiberglass.

So, let's say you live in Wisconsin, and the R-value required is 49; According to this study, 16.3" of fiberglass (R-Value 49) would only perform about as well as 4" of foam (R-Value 25). In other words, requiring 49 R-value in foam is unfair because you only need about 1/3 the thickness of foam (or 1/2 the R-value) for the same, or better performance.

49 R-Value Fiberglass: at 3-R per inch, you need 16.3 inches of blown fiberglass to reach R-49
25 R-Value Foam: just 3.92" to 4" inches of sprayed-in foam! (this perfoms equal to R-49 in blown fiberglass)

Summary: SPF Foam outperforms fiberglass by 40-50% in extreme weather conditions. In other words, you need nearly about twice as much R-Value in fiberglass to match the same R-value in foam. In this case, just 5.5 inches of low density foam (R-Val 34) outperformed fourteen inches of blown fiberglass (R-Val 42)!

R-Value Comparison Chart

Here are some typical R-Value Comparisons of various insulation products and materials.

Insulation Materials
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Material Type R-Value Per Inch
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Fiberglass Batt 3.14-4.30
Fiberglass Blown (attic) 2.20-4.30
Fiberglass Blown (wall) 3.70-4.30
Rock Wool Batt 3.14-4.00
Rock Wool Blown (attic) 3.10-4.00
Rock Wool Blown (wall) 3.10-4.00
Cellulose Blown (attic) 3.13
Cellulose Blown (wall) 3.70
Vermiculite 2.13
Autoclaved Aerated Concrete 1.05
Urea Terpolymer Foam 4.48
Rigid Fiberglass (> 4lb/ft3) 4.00
Expanded Polystyrene (beadboard) 4.00
Extruded Polystyrene 5.00
Polyurethane (foamed-in-place) 6.25
Polyisocyanurate (foil-faced) 7.20

Here's a visual R-Value Representation:

You can ignore the K-factor; the chart is really just to display some R-value comparisons. If are curious heres the definition of K-Factor: a thermal insulation value coefficient of thermal conductivity, which describes the amount of heat that passes through a unit cube of material in a given time when the difference in temperature across the cube is one degree.

Example of a Performance Based Building Code

Not all regulations are focused on R-value due to the inaccuracies explained above. Here's an example of a more performance based building code (r-value is not mentioned, just temperatures, and preventative measures). Polyurethane Spray Foam insulation contractors have been frustrated for years with high R-Value requirements for homes in northern colder climates. Here are some sample insulation requirements for an attic in Salt Lake City, Utah, which happens to fall into Zone 5. The 2006 International Residential Code (Sec. R806.4) states that unvented roofs in Zone 5 must pass three criteria:
1-Interior vapor retarders may not be installed on the ceiling side (below the attic) of the un-vented attic assembly
2-Air-Impermeable insulation must be applied directly to the underside of the structural roof deck (i.e., on the inside of the house)
3-Sufficient insulation must be installed to maintain monthly avg temp of the condensing surface (the interior of the attic) above 45 degrees Fahrenheit.
In summary, your contractor needs to install the insulation on the underside of the roof deck inside your attic (so the bottom side of your roof inside your house). The insulation must be capable of maintaining an interior surface temp of 45 deg. Fahrenheit (to prevent condensation, rotting, etc). Anyway, a review of the core requirements of the Zone 5 code don't mention R-value at all, just temperature and performance requirements.

Spray Foam Insulation Cost Estimate (California Bay Area)

IF you live in the Bay Area, you can get a cost estimate on Spray Foam Insulation here. This contractor has three decades of experience, and exceptional ratings from value star, diamond certified, and has been on the BBB honor roll continuously for many years. They are a trusted source of information as well, and have provided articles for major publications such as Eichler Network.

It's a little dense at times, but overall I found this article very interesting. I only wonder why it has taken so long for the government to adjust to allow SPF foam roofing when it's obviously a technologically superior product.

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