Phenolic Foam Insulation Revisited

A particularly well-thought-out and thorough question from longtime GBA reader Aaron Birkland regarding the pH of phenolic foam and its possible corrosive properties prompted me to revisit my original blog on Kingspan's Kooltherm rigid insulation.

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Aaron has two main questions:

• Has the issue of acidity and corrosion of fasteners or metal roof decks been resolved with Kingspan's Kooltherm?
• If so, is Kooltherm the only option for phenolic foam rigid insulation?

Brief Background

Phenolic foam rigid insulation was introduced in the U.S. in the 1980s by Beazer East and Johns Manville. However, serious corrosion issues led to legal actions, resulting in both companies ceasing production in the mid-1990s.

Kingspan, an Irish company, developed a completely new formulation for its phenolic foam insulation. They began producing and selling Kooltherm in Europe in 1988 and introduced it to the U.S. market in 2014.

The Dow Report

In 2016, Dow Building Solutions presented a white paper titled "Rigid Polymeric Foam Boardstock Technical Assessment" at a Society of Plastics Engineers conference. This paper compares the performance properties of two types of phenolic foam, one type of polyisocyanurate, and one type of extruded polystyrene (XPS) insulation. Here are the key takeaways from the paper:

1. None of the two phenolic foam board insulations mentioned in the Dow white paper is Kingspan's Kooltherm.
2. The R-value for the phenolic foam boards is rated between R-6.7 and R-7.5 per inch, while Kooltherm insulation boasts an R-value of R-8+ per inch. Since Kooltherm's cell structure is not uniform, its actual R-value can vary based on thickness.
3. The residual formaldehyde in the phenolic foam boards discussed ranges from 137 to 253 parts per million (ppm). Kingspan has independent third-party data (from the Fraunhofer Institute in Germany) indicating residual formaldehyde levels below 0.15 ppm. However, as a Europe-based company, Kingspan currently lacks U.S. standardized test results.
4. The paper reports pH results according to ASTM 971, with phenolic insulation A at 2.7 and phenolic insulation B at 2.0, both quite acidic. Kingspan claims Kooltherm tests yield a pH similar to polyiso, ranging from 3.8 to 4. The absence of third-party ASTM results remains a challenge that Kingspan is actively addressing with U.S. testing agencies.

Dr. Jan Kosny of the Fraunhofer Institute and a recognized expert in building science characterized the Dow report as "marketing material."

Kingspan provided a third-party pH test for their Kooltherm insulation conducted by Cardiff University on July 21, 2016, following the EN testing method. Two samples yielded pH results of 6.51 and 6.49.

Kingspan's BDA Keuringsinstituut Test Report

Kingspan shared a test report prepared by BDA Keuringsinstituut (a division of Kiwa NV, a Netherlands-based testing laboratory) dated January 22, 2018. While I cannot fully disclose the report, here are some insights.

In the BDA Keuringsinstituut tests, four types of rigid insulation—mineral wool, Kingspan phenolic foam, polyurethane (PUR), and expanded polystyrene (EPS)—were installed on a profiled steel deck and covered with an EPDM roof membrane. These assemblies were subjected to 70°C (158°F) and 95% relative humidity for 28 days.

From the "Results" section of the report: "[I]t appears that there is no structural difference in the amount of corrosion after the test. All screws showed an average of the same amount of corrosion on the part that penetrated the profiled steel deck. The portion not in contact with the deck and directly exposed to the insulation material exhibited no corrosion."

I attempted to contact Dow Building Solutions for their response to the BDA Keuringsinstituut report on Kingspan's Kooltherm but did not receive a reply.

My "Wingnut Testing"

In an effort to investigate corrosion, I visited a Kooltherm project in Brattleboro and removed screws to check for any corrosion. However, these large screws had a baked enamel finish and had only been in place for about four or five months.

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I also remembered using Kooltherm in a wall mockup during my blog on the X-Floc cellulose insulation installation system. This mockup, installed with regular drywall screws, has been sitting in my damp garage for the last three months, and there is still no sign of fastener corrosion. I filled the drywall screw holes with water and reinserted the screws; a week later, there was no corrosion.

DOE Buildings Technology Office Project on Phenolic Foam Insulation Development

I was previously unaware of the DOE Buildings Technology Office project, which focuses on the development of a bio-based, inexpensive, non-corrosive, and non-flammable phenolic foam for building insulation. I reached out to project partner Atlas Roofing, who informed me that there has been no commercialization of this work or any new patents resulting from the project.

Before completing this blog, I connected with Dr. Jan Kosny, Director of Building Enclosures and Materials at the Fraunhofer Institute U.S.A. Kosny shared the following:

1. The DOE project was completed in 2018. Currently, Fraunhofer is funded by the DOE and is working with Oak Ridge National Laboratory on corrosion field testing for a variety of phenolic foam insulations, research set to conclude in 2021.
2. As part of the corrosion field testing, Fraunhofer has a rooftop test hut for 5 or 6 commercially available phenolic foam insulations and two new formulations.
3. Fraunhofer is continuing its independent research into phenolic foam insulation, which involves sustained multi-year product development.
4. Although Atlas Insulation is no longer participating in this development effort, Fraunhofer is in serious discussions with several other companies to advance phenolic foam insulation development.

It's evident that these images (and the accompanying testing) far surpass my "Wingnut-testing."

Conclusions

Kooltherm remains the leading phenolic foam rigid insulation currently available in the U.S.

Concerns regarding acidity and corrosion have been effectively addressed with Kooltherm phenolic foam rigid insulation. While there may not be competitors available immediately, ongoing research and development could usher in serious competition in the future.

In addition to serving as GBA's technical director, Peter Yost is the Vice President for Technical Services at BuildingGreen in Brattleboro, Vermont. With over twenty years of experience in building, researching, teaching, writing, and consulting on high-performance homes, he has been recognized as NAHB Educator of the Year. If you have a building science inquiry, you can contact Pete here. You can also sign up for BuildingGreen's newsletter to receive a free report on insulation and regular updates from Peter.

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