The Best Insulation for Homes - 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



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



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

4” XPS



Unfaced Fiberglass batt and 6 mil polyethylene vapor barrier

5.5” of fiberglass



Closed-cell spray foam (control)




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



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 would not influence other test bays by conduction through the studs.

3. I tried to make all the test bays exactly the same but because if 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. I can also be used to approximate the performance of the building shell on a windy day and on a very cold day.

Return to Best Insulation for Homes page from Best Insulation Test page
Go to Flash and Foil Results
Go to XPS and Foam Sealant Results
Go to Fiberglass Results
Go to Spray Foam Results
Go to Flash and Batt Results
My Conclusions