Spray foams like Icynene boast high performance, but haven't been able to catch fiberglass batts in market share.
Spray foams like Icynene boast high performance, but haven't been able to catch fiberglass batts in market share.

Two recent studies regarding home insulation products shed light on shifts in this highly competitive market. One of these studies quantified the evolving market shares of fiberglass and spray foam, while the other raised questions about which product offers the best real-world thermal value for a given wall thickness. While some of the conclusions may be surprising, both studies indicate that fiberglass batts aren’t likely to lose their standing at the top of the field any time soon.

Although fiberglass batts have never fallen from their perch as the dominant insulation used in North American homes, spray foam products have posed a serious challenge in recent years. Because foam acts as an air sealer as well as an insulator, it has made inroads among performance-oriented builders, especially those building high-end custom homes for demanding customers. That, along with the International Energy Code's new requirement that homes be tested for air leakage, helped spray foam expand its market share. Now that share seems to have collapsed. 

The collapse was identified by the 2014 Builder Practices Survey, published by Home Innovation Research Labs in Upper Marlboro, Md. (formerly the NAHB Research Center). The annual survey, which tracks sales of dozens of building materials, saw spray foam’s share grow from 3% in 2008 to 11% in 2012. The next year, however, it abruptly fell back to 8%, with fiberglass batts capturing most of the loss. 

Those results seem consistent with a separate 2013 study conducted by Home Innovation Research Labs that found 30% of builders who used spray foam in the past have switched back to batts. "We often hear builders state that fiberglass, the most popular home insulation material, is simply the most cost-effective, easy-to-install material," a press release issued by the lab stated. 

The most likely reason behind this shift is simple economics, according to the study. For one thing, since the recession, home buyers have been tightening their budgets across all product categories. Additionally, multifamily rental housing, which favors less expensive materials, has grown as a percentage of construction starts.

But a switch back to fiberglass batts doesn't have to equal poorer performance, according to The Thermal Metric Summary Report released this summer by Building Science Corporation (BSC) in Westford, Mass. The report details a multi-year project, sponsored by a consortium of insulation manufacturers, that measured how 13 different wall assemblies using a variety of insulation products performed at various temperatures and air pressures. The wall assemblies were built and tested at Building Science Labs in Waterloo, Ontario, at temperatures ranging from 144 degrees F to -18 degrees F. Insulations used included fiberglass batts as well as open- and closed-cell spray foam products. Chris Schumacher, the researcher who headed the project, says that he used a test method that measures heat and airflow through a wall while conditions are held stable for 24-48 hours. 

Some of the sponsors have put their own spin on the results, while others have challenged results that shed an unfavorable light on their product.

One interesting finding that no one has challenged is that the R-value of all insulation products varies with temperature: the colder it gets, the more effective the insulation. For instance, in one test a wall with R-15 fiberglass batts delivered an actual value of R-14 at the coldest temperatures; that number fell to R-10.4 at the hottest settings. (The actual R-value of a wall with between-the-studs insulation will always be lower than the insulation's nominal R-value because of thermal bridging through framing members.) The results for open-cell foams were similar. 

The results that have caused some disagreement hinge on the issue of workmanship. The study found that when a fiberglass-insulated wall has been properly air sealed, its thermal performance equals that of spray foam. "The findings show that as long as you do a good job air sealing, an R-13 wall is an R-13 wall regardless of the insulation used," says Charles Cottrell, vice president of technical services with the North American Insulation Manufacturers Association (NAIMA), the trade group for fiber glass, rock wool, and slag wool insulation products, and one of the study's sponsors. He adds that the fiberglass-insulated wall assemblies were sealed with an off-the-shelf latex caulk.

Not surprisingly, the foam industry takes issue with NAIMA's assertion. Open-cell foam manufacturer Icynene, another sponsor of the study, doubts that the lab conditions represent actual home building practices. "We question if the test walls insulated with fiberglass and sealed with latex represent typical field construction practice and provide useful test results," says John Broniek, an Icynene senior engineer. 

BSC's Schumacher echoes that reservation. "Do those walls represent what's being done in the field?" he asks. "We don't know." He points out that each test wall in the study was insulated by the representative of that insulation using the best practices available, and that there's no objective measure of how typical those practices are. "As an industry, we don't have a good statistical sampling of what's happening in the real world." 

NAIMA's Cottrell counters that workmanship issues apply to all materials, and points out that that some of the foam-insulated walls in the study showed voids between the foam and the sheathing when disassembled after the tests. Despite these voids, the Icynene wall was the most airtight of those studied, with one-quarter the air leakage of the fiberglass batt wall at extremely cold temperatures.

Whichever way the market goes, customer expectations and stricter codes will gradually raise the thermal requirements for new homes. Either method of insulation is capable of meeting those requirements, but the workmanship standards for getting there will only get higher.