Blog Post

Phenolic Foam Insulation Revisited

Can we put to bed the corrosion concerns with this insulation?

Slideshow (click to launch)

Photo of four types of rigid insulation

Four types of rigid insulation  are fastened to a steel deck. Clockwise from upper left: EPS, mineral wool, polyurethane, and phenolic foam insulation.

Image: BDA Keuringsinstituut - Kiwa NV
A particularly well thought-out and thorough question from reader Aaron Birkland on the pH of phenolic foam and its possible corrosive nature prompted me to follow up my original blog post on Kingspan’s Kooltherm rigid insulation. Aaron has two main questions:

  • Has the issue of acidity and corrosion of fasteners or metal roof decks been solved with Kingspan’s Kooltherm?
  • If so, is Kooltherm the only phenolic foam rigid insulation game in town?

Brief background

Phenolic foam rigid insulation was introduced in the U.S. in the 1980s and sold by Beazer East and Johns Manville, but serious corrosion problems resulted in legal action, and both companies ceased production in 1992.

Kingspan, an Irish company with a completely new formulation for its phenolic foam insulation, has been producing and selling Kooltherm in Europe since 1992, introducing it in the U.S. in 2016.

The Dow report

In 2012, Dow Building Solutions introduced a white paper, “Rigid Polymeric Foam Boardstock Technical Assessment,” at a Society of Plastics Engineers conference. This paper compares certain performance properties of two types of phenolic foam, one type of polyisocyanurate, and one type of extruded polystyrene (XPS) insulation. Here are the most important points from this paper:

  1. Neither of the two phenolic foam board insulations mentioned in the Dow white paper is Kingspan’s Kooltherm.
  2. The listed R-value for the phenolic foam boards is R-6.7 to R-7.5 per inch; Kooltherm insulation is R-8+ per inch. (Since the cellular structure of Koolspan’s phenolic foam is not uniform, the actual per-inch R-value of the insulation varies depending on thickness.)
  3. The residual formaldehyde in the phenolic foam board discussed in the paper ranges from 137 to 253 parts per million (ppm). Kingspan does not report residual formaldehyde content but does have independent third-party data (testing conducted by the Fraunhofer Institute in Germany) showing formaldehyde emissions at less than 0.15 ppm. (One difficulty is that as a Europe-based company, Kingspan does not yet have U.S. standardized test results.)
  4. The paper reports pH results per ASTM 971 for phenolic insulation A of 2.7 and for phenolic insulation B of 2.0 (quite acidic). Kingspan claims that Kooltherm tests yield pH in the same range as polyiso – 3.8 to 4. Again, the lack of third-party ASTM results is a current issue that Kingspan is working on with U.S. testing agencies.

Dr. Jan Kosny of Fraunhofer Institute (see last section of this blog post) is a widely respected building scientist and materials expert; Kosny characterized this Dow report as “marketing material.” Kingspan provided me with a third-party pH test of their Kooltherm insulation conducted by Cardiff University, dated July 21, 2010, following the test method for EN13468: “Thermal insulating products for building equipment and industrial installations - Determination of trace quantities of water soluble chloride, fluoride, silicate, and sodium ions and pH.” Two samples of the insulation yielded pH test results of 6.51 and 6.49.


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Kingspan’s BDA Keuringsinstituut test report

Kingspan shared a test report with me prepared by BDA Keuringsinstituut (a division of Kiwa NV, a Netherlands-based testing laboratory), dated January 22, 2010. I do not have permission to copy or post this full report, but below is information from the report. For the BDA Keuringsinstituut tests, four types of rigid insulation — mineral wool, Kingspan phenolic foam, polyurethane (PUR), and expanded polystyrene (EPS) — were fastened with washers and screws to a profiled steel deck (see Image #1, above) and the insulation then covered with an EPDM roof membrane (see Image #2 in the slideshow). These assemblies were then placed over a heated water tank such that the assemblies were subjected to 70°C (158°F) and 95% relative humidity for 28 days. To see the condition of the fasteners after testing was complete, see Images #3, #4, and #5 in the slideshow (all photos taken from the report). From the “Results” section of the report: “….[I]t appears as though there is no structural difference in the amount of corrosion after the test. All screws show on average the same amount of corrosion on the part of the screw that has been turned through the profiled steel deck. On that part that has not been turned through the profiled steel deck and therefore was in direct contact with the insulation material no corrosion was found.” I tried to contact Dow Building Solutions to get their response to the above BDA Keuringsinstituut report on Kingspan’s Kooltherm, but did not hear back.

My “Wingnut testing”

It dawned on me that I could go to the Kooltherm project right here in Brattleboro, climb into the unfinished attic, and back out some screws to see if there was any corrosion (see Images #6 and #7). The only problem is that those big bad-boy screws were protected by a baked enamel finish, and they have only been in place about 4 or 5 months. I also remembered that for my blog post on the X-Floc cellulose insulation installation system, we used Kooltherm in a wall mockup installed with plain old interior drywall screws (see Images #8 and #9). This wall mockup has been sitting in my quite damp garage for the last three months. There is still no fastener corrosion, so I decided to fill the drywall screw holes with water and put the screws back in (see Image #10). Image #11 shows the same screw a week later: no corrosion, for what it’s worth.

DOE Buildings Technology Office project on phenolic foam insulation development

I was not aware of the DOE Buildings Technology Office project until Aaron let me know about it: Development of a Bio-based, Inexpensive, Noncorrosive, and Nonflammable Phenolic Foam for Building Insulation (see Image #12). I checked in with the project partner, Atlas Roofing. They reported that there has been no commercialization of this work, either on their part or as evidenced by any new patents they could find based on this project (a key indicator of any project commercialization). Just before completing this blog post, however, I did reach Dr. Jan Kosny, Director of Building Enclosures and Materials at the Fraunhofer Institute U.S.A. Kosny reports:

  1.  This DOE project was completed in 2017. Currently Fraunhofer is being funded by DOE and working with Oak Ridge National Laboratory on corrosion field testing of a range of phenolic foam insulations, research that will be completed in 2019.
  2.  As part of the corrosion field testing, Fraunhofer has a rooftop test hut for five or six commercially available phenolic foam insulations as well as two new formulations (see Images #12 and #13).
  3. Fraunhofer is independently continuing its work on phenolic foam insulation, a process that involves sustained multi-year product development (up to eight more years).
  4. While Atlas Insulation is no longer involved in this product development effort, Fraunhofer is serious and is engaged in confidential discussions with a number of other companies to continue phenolic foam insulation development.

Not surprisingly, these images (and the testing they represent) put my “Wingnut testing” to shame.


Kooltherm remains the “real McCoy” of currently available phenolic foam rigid insulation in the U.S. Acidity concerns and corrosion issues have been resolved with Kooltherm phenolic foam rigid insulation. And while competitors to Kooltherm insulation may be several years out, Fraunhofer-led research and development could well mean serious competition in the years to come.


Published July 13, 2018

Yost, P. (2018, July 13). Phenolic Foam Insulation Revisited. Retrieved from

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