The Best Insulation for Homes, My Experiment

I know it’s hard to decide when it comes to choosing the best insulation for homes and buildings.  R-value is describes the conductive heat loss of different types of insulation but what about heat loss due to convection(wind and air leakage) and radiant heat loss?  Even if you have a good handle on the physics of heat flow, it is still hard to sort the hype from the facts.  Every brand lists its advantages as indisputable facts buttressed by charts, graphs and independent research.  It is easy to wonder what the facts really are.  I designed a simple experiment to cut through some of that.     

I am sure that other experiments exist that are more rigorous than mine but I have not found them in the public domain.  Especially interesting to me, there is very little research on radiant barriers and combination insulation systems.   So, I needed some answers for myself.  I hope you will share these results far and wide with your friends.  Feel free to make a link to this page. 

I should warn you that the results are surprisingly dull.  I have not exposed some fraud on the part of a manufacturer or debunked the R-value rating system.  In fact, this experiment has just reaffirmed my position that all insulation products have strengths and weaknesses.  Our job is to understand those strengths and weaknesses well enough meet the goals of the project and prevent failures down the road.

While I am confident that my experimental design stands up to peer review I concede that I was not able to set up the very best experiment possible.  I do not have a research lab, if you want to throw a couple million my way I’ll gladly start one.
 

The chart below summarizes the insulation systems I tested.

Insulation system

Thickness

R-value/inch

Total R-value

Flash and Foil- closed cell spray foam and aluminum baffle radiant barrier.  The foil barrier has small holes in it so it is not a vapor barrier to avoid a double vapor barrier condition.  

2” of spray foam with a radiant foil barrier stapled to the studs of a 2x6 wall bay.  The foil barrier has 2 foil baffles separated by air.

6.24 for the spray foam and R 7.66 equivalent R-value for the foil barrier

20

 

Extruded polystyrene (XPS) and one-part foam sealant (can foam)

4” XPS

5

20

Unfaced Fiberglass batt and 6 mil polyethylene vapor barrier

5.5” of fiberglass

3.45

19

Closed-cell spray foam (control)

3.25”

6.24

20

Flash and Batt - closed cell spray foam and  unfaced fiberglass batt

2” of spray foam and 2.5” of fiberglass batt

6.24 for the foam and 3.45 for the fiberglass

21

 


Results:

Click on the links below to see the images showing the results. I warned you they would be dull, I should have modified them just to stir up some controversy in the industry. I have arranged the photographs so you can see how each insulation system was installed, how it was covered, how it compares to the control under normal conditions and under depressurization. Pretty straight forward.

Remember, as you review these pictures you are comparing the test bay to the control bays (R20 closed-cell spray foam) on either side of it. Every test bay is compared to the same control bay.

When you are done looking at each system click below to get my conclusions from the experiment.

Flash and Foil Test Results
XPS and Foam Sealant Test Results
Fiberglass Test Results
Spray Foam Test Results
Flash and Batt Test Results
My Conclusions from the Tests
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For those of you that want the technical nitty gritty, read on. If you're not into that just hop to results and conclusions links above. Truth told, I hardly ever read the "methods" section in scientific papers.

Experimental Design:

The goal of the experiment was to test the following insulation systems against each other in the real world. I chose the systems listed below so that I could compare very common systems such as fiberglass with systems that are less common and have very little research history.

Insulation system

Thickness

R-value/inch

Total R-value

Flash and Foil- closed cell spray foam and aluminum baffle radiant barrier.  The foil barrier has small holes in it so it is not a vapor barrier to avoid a double vapor barrier condition.  

2” of spray foam with a radiant foil barrier stapled to the studs of a 2x6 wall bay.  The foil barrier has 2 foil baffles separated by air.

6.24 for the spray foam and R 7.66 equivalent R-value for the foil barrier

20

 

Extruded polystyrene (XPS) and one-part foam sealant (can foam)

4” XPS

5

20

Unfaced Fiberglass batt and 6 mil polyethylene vapor barrier

5.5” of fiberglass

3.45

19

Closed-cell spray foam (control)

3.25”

6.24

20

Flash and Batt - closed cell spray foam and  unfaced fiberglass batt

2” of spray foam and 2.5” of fiberglass batt

6.24 for the foam and 3.45 for the fiberglass

21

 

 

To make the comparison fair I did the following:

1.     All the insulation systems have approximately the same R-value.

2.     I distributed all the test bays along the west wall of my addition so that each test bay was bordered on either side by a control bay, in this case 3.25” of closed-cell spray foam. I did this in case one insulation system performed so differently than the others it could not influence other test bays by conduction through the studs.

3.     I tried to make all the test bays exactly the same but because of outlets and switch boxes I was not always able to. If wiring penetrations were part of a test bay I sealed them with foam so that air leakage through the studs would be eliminated.

4.     I compared the bays with infrared images and infrared temperature readings all collected after 9:00 pm at night to rule out solar effects. All images were shot from the inside because thermal imaging is generally clearer from inside. I used a Fluke TiR1 infrared camera.

5.     All the insulation systems were covered with ½” of sheetrock with taped and mudded seams. There was no paint on any of the sheetrock.

6.     Imaging was done on a night when the wind was calm. The outside air temperature was 10° F (-12.2 ° C) and the inside temperature was 55° F (12.8 ° C).

7.     All the insulation systems were tested under normal conditions and depressurization to 50 Pascals which is roughly equivalent to a 20 mph wind. Depressurization is not the natural state of most buildings (at least it shouldn’t be) but it is done to identify the effects of air infiltration on a building. It can also be used to approximate the performance of the building shell on a windy day and on a very cold day.

 

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