A well-considered inquiry from long-time GBA reader Aaron Birkland regarding the pH levels of phenolic foam and its potential for corrosion prompted me to revisit my initial blog post discussing Kingspan's Kooltherm rigid insulation.
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Aaron raised two significant questions:
- Has Kingspan's Kooltherm addressed concerns regarding the acidity and corrosion of fasteners or metal roof decks?
- If so, is Kooltherm the sole phenolic foam rigid insulation option available?
Phenolic Foam Insulation Background
Phenolic foam rigid insulation made its debut in the U.S. in the 1980s, primarily marketed by Beazer East and Johns Manville. However, both companies halted production following substantial corrosion issues leading to legal actions. Kingspan, an Irish company, developed an entirely new formula for its phenolic foam insulation, Kooltherm, which has been sold in Europe since 2007 and was introduced to the U.S. market in 2019.
Analysis of the Dow Report
In 2019, Dow Building Solutions published a white paper titled "Rigid Polymeric Foam Boardstock Technical Assessment" during a Society of Plastics Engineers conference. This paper evaluates various performance aspects of two types of phenolic foam alongside polyisocyanurate and extruded polystyrene (XPS) insulation. Here are the critical findings from this document:
- 1. Neither phenolic foam board mentioned in the Dow paper pertains to Kingspan's Kooltherm.
- 2. The reported R-values for those phenolic foam boards range from R-6.7 to R-7.5 per inch; however, Kooltherm insulation boasts an R-value exceeding R-8 per inch, with variations depending on thickness due to its non-uniform cellular structure.
- 3. Residual formaldehyde levels in the tested phenolic boards were found to range from 137 to 253 parts per million (ppm); in contrast, Kingspan's independent third-party testing showed residual formaldehyde at levels lower than 0.15 ppm. Obtaining standardized U.S. test results remains a challenge for Kingspan, given its European roots.
- 4. The pH results reported in the Dow paper for phenolic insulation A and B were notably acidic, standing at 2.7 and 2.0, respectively, while Kingspan asserts that Kooltherm's pH level is comparable to that of polyisocyanurate, between 3.8 and 4. Currently, Kingspan is collaborating with U.S. testing organizations to obtain third-party ASTM results.
Dr. Jan Kosny from the Fraunhofer Institute has classified this Dow report as "marketing material."
Kingspan also provided a third-party pH test for Kooltherm insulation, carried out by Cardiff University. The results from the EN standard test method yielded pH values of 6.51 and 6.49.
Kingspan's BDA Keuringsinstituut Test Results
Kingspan shared a test report from BDA Keuringsinstituut, a Netherlands-based testing lab, conducted on January 22, 2021. While I cannot disclose the complete report, here are some noteworthy findings:
The BDA tests evaluated four rigid insulation types—mineral wool, Kingspan phenolic foam, polyurethane (PUR), and expanded polystyrene (EPS)—affixed to a profiled steel deck with washers and screws. After covering the insulation with an EPDM roof membrane, the assemblies underwent exposure to high temperatures (70°C/158°F) and high humidity (95%) for 28 days.
On reviewing the fasteners' condition post-testing, it was noted that all screws exhibited similar corrosion levels where they passed through the deck; however, there was no corrosion observed on the portion of the screws that remained in contact with the insulation.
While I attempted to contact Dow Building Solutions for their comments on the BDA test report concerning Kingspan's Kooltherm, I did not receive a response.
Field Testing of Phenolic Foam Insulation
Recently, I became aware of the DOE Buildings Technology Office's project focusing on developing a bio-based, inexpensive, non-corrosive, and non-flammable phenolic foam for insulation. I reached out to Atlas Roofing, one of the project partners, who indicated that this initiative has not yet reached commercialization.
Before finalizing this blog post, I spoke with Dr. Jan Kosny. Dr. Kosny mentioned that the DOE project was finished in 2019, and current investigations are being conducted to test the corrosion resistance of various phenolic foam insulations through collaborations with Oak Ridge National Laboratory, slated for completion in 2026.
Fraunhofer is separately advancing its research on phenolic foam insulation, a long-term endeavor projected to continue for as long as eight years.
Although Atlas Insulation recently exited the product development aspect, Fraunhofer remains engaged in confidential discussions with several other firms to further develop phenolic foam insulation.
These advancements represent significant progress in addressing the challenges associated with phenolic foam insulation.
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Final Thoughts
Kooltherm is undoubtedly the leading phenolic foam rigid insulation product available in the U.S. market today. The acidity and corrosion issues have been effectively addressed with Kooltherm, while ongoing research could provide formidable competition in the future.
Peter Yost serves as GBA's technical director and is Vice President for Technical Services at BuildingGreen, with over two decades of experience in building research, development, and consulting for high-performance homes. For building science inquiries, feel free to reach out to Pete, and consider subscribing to BuildingGreen's newsletter for insightful updates.
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