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Building Science

Kingspan Kooltherm Phenolic Foam Rigid Insulation

A deep-energy-retrofit project uses Kooltherm as part of a high-performance attic insulation system

A type of rigid foam insulation called Kingspan Kooltherm was installed as part of the energy retrofit work at this house in Brattleboro, Vermont. The house has a slate roof.
Image Credit: Images #1, #4, #5, #6, and #7: Peter Yost
View Gallery 7 images
A type of rigid foam insulation called Kingspan Kooltherm was installed as part of the energy retrofit work at this house in Brattleboro, Vermont. The house has a slate roof.
Image Credit: Images #1, #4, #5, #6, and #7: Peter Yost
The existing roof assembly was pretty typical, until the R-value was beefed up to R-53. The interior Kooltherm contributes R-32, and the dense-packed cellulose contributes R-21.
Image Credit: Image #2: Eli Gould, PreCraft
These micrographs show the unique shape and quality of the closed cell structure of Kooltherm.
Image Credit: Image #3: Kingspan
Workers are insulating the second floor and attic at 81 Chapin Street with Kooltherm. There are two layers on the interior of the roof slopes and one layer on the walls. Seams are taped for airtightness. The Kootherm insulation in the attic space can be left exposed, since according to code authorities, the insulation qualifies as an ignition barrier. Note that large gaps in the wall sheathing have been air-sealed with spray foam before the Kooltherm rigid insulation was installed on the interior of the walls. After the first layer of Kooltherm was installed, a worker from American Installations uses the company's innovative cellulose installation system to achieve a dense installation of cellulose in the roof framing cavities. This process will be the topic of the next blog on the 81 Chapin Street deep energy retrofit.

Improving the thermal performance of an existing attic is often challenging: workers are faced with narrow cavities, low clearances, and cladding systems that make it hard to achieve desired R-values while still maintaining the necessary drying potential of the assembly.

The house at 81 Chapin Street in Brattleboro, Vermont, is no exception. It’s a 100-year-old wood-framed two-story home that Alex Beck and Candace Pearson are determined to comprehensively retrofit to high performance.

That’s where Eli Gould, owner and founder of Ironwood Brands, comes in. Eli is an architect and builder responsible for projects like the Lemon’s “Almost” Passive House and Alex and Jerelyn Wilson’s Leonard Farm retrofit (see multiple GBA Energy Solutions blogs on the Wilson project). The Brattleboro project has no shortage of challenges; for example, in subsequent blogs we will discuss the basement. Here, we’ll focus on the attic, which needed careful hygrothermal consideration.

Eli Gould lays out the roofing configuration used at 81 Chapin Street: “We decided to cavity fill with dense-packed cellulose and then — on the underside of the rafters — to run two staggered-seam, taped layers of 30 mm foil-faced rigid foam insulation.” Gould specified Kingspan Kooltherm rigid foam. (Kingspan is an international corporation headquartered in Ireland. Kingspan’s U.S. office is located in Atlanta, Georgia. Kooltherm is a type of rigid foam called phenolic foam.)

[Editor’s note: Phenolic foam rigid insulation was introduced in the U.S. in the 1980s and sold by Beazer East and Johns Manville. Serious corrosion problems of fasteners and steel decks that were in contact with the foam resulted in legal action, and both companies ceased production of phenolic foam in 1992. For more information on the history of phenolic foam marketing in the U.S., see Phenolic Foam Insulation Revisited.]

He continued, “This approach got us to the right total R-value, highest level of airtightness, and excellent drying potential to the exterior.” The exterior layers of the roof assembly include sheathing boards, building paper, and slates. Gould added, “And the clincher for the attic was that the foil-faced Kootherm up there does not need any ignition barrier.”

Candace Pearson, a former editor and research analyst for BuildingGreen, explained, “Initially, we were hoping to find a wood fiberboard insulation that could be installed to the interior [of the rafters], but when we did the modeling we found out we needed a higher R-value.”

Candace said, “We became interested in Kooltherm because, unlike XPS, Kooltherm did not use a high global warming potential (GWP) blowing agent and, unlike conventional polyiso, it did not contain added chemical flame retardants. That’s what initially prompted me to suggest the product. Plus, it is a recommended product in the latest BG insulation guide.”

Kooltherm characteristics and properties

Alex Wilson of BuildingGreen has already published a great article on Kooltherm. The details are really a bit hard to believe:

  • R-6.2 per inch for 1-inch samples, and R-8.2 per inch for 3-inch samples — R-values that are third-party-certified per IECC Section C402;
  • No flame retardants yet exceptional smoke development and flame development numbers;
  • Zero ozone depletion potential (ODP);
  • Low global warming potential (GWP).

Let’s go after the first two of these (the most difficult to accept, frankly).

R-value claims

You get R-6.2 or R-6.3 per inch for 1-inch samples, and R-8.2 per inch for 3-inch samples, according to the manufacturer, because of two properties of Kooltherm:

  • The insulation includes really tiny gas pockets (the smaller the pockets, the less heat flow); and
  • The insulation has a high percentage of closed cells (98% are truly trapped gas pockets).

Here is a link to a good technical reference from Kooltherm.


I have the most trouble with the flammability performance claimed for Kooltherm. After all, it’s a petroleum-based polymer matrix with a hydrocarbon blowing agent. It seems as though we are getting burned, not the insulation!

When I asked Kingspan about this, they stated that phenolic foam is “inherently flame-resistant.” That seemed like restatement, not an explanation. I was then referred to one of Kingspan’s chemists, who explained it this way: “It [comes] down to the highly cross-linked thermoset PF [phenol formaldehyde] material. [With] a phenolic matrix, unlike U-F chemistry, once cured the polymeric thermoset material is irreversible. Phenolic resins … have a highly cross-linked, high carbon (char), and aromaticity level which lends itself to excellent FST (fire, smoke, and toxicity) properties. The material is stable to well over 200°C.”

That seems to address the fire properties of the phenolic foam matrix, but what about the pentane blowing agent? Craig Lynch, commercial technical director at Kingspan, responded, “The Kooltherm blowing agent is not pentane, but pentane-based. The actual blowing agent is a proprietary mix, with constituents added to — among other things — reduce the flammability of the blowing agent.”

That makes some sense to me as well, but is not wholly convincing. Being an empirical sort of guy, I decided to torch some Kooltherm.

Using a grill starter flame source, the test yields no flame, very little smoke, and only charring.

Using a propane torch, the test yields no flame, very little smoke, and only charring.

That’s pretty impressive fire resistance with both the low-temperature grill starter and the higher temperature propane torch.

Test results

To be completely fair, here is a list of fire performance standardized tests from the laboratory certification for NFPA 286: “Tested Wall Assemblies Using Kingspan Kooltherm Insulation Boards in Attics, Crawlspaces, Basements, and other Interior Applications.”

The NFPA 286 test is the “corner” test for interior applications (for example, see this video). The NFPA 285 test is the exterior assembly test (for example, see this video).

  • Performance in accordance with ASTM E84/UL 723 for smoke and flame development: Flame Spread Index <25; Smoke Developed Index <450
  • Performance for use without a thermal barrier in accordance with IBC Section 2603.4 and 2603.5.2: Approved.
  • Performance with regard to vertical and lateral fire propagation in accordance with IBC Section 2603.5.5: Approved.
  • Performance with regard to ignition in accordance with IBC Section 2603.5.7: Approved.

Clearly Kooltherm — notwithstanding that it is a directly derived petroleum-based rigid insulation — has solid high-performance credentials.

Gould concludes, “Kooltherm is now my interior rigid insulation material of choice for this type of deep energy retrofit.”

In addition to acting as GBA’s technical director, Peter Yost is the Vice President for Technical Services at BuildingGreen in Brattleboro, Vermont. He has been building, researching, teaching, writing, and consulting on high-performance homes for more than twenty years. An experienced trainer and consultant, he’s been recognized as NAHB Educator of the Year. Do you have a building science puzzle? Contact Pete here. You can also sign up for BuildingGreen’s email newsletter to get a free report on insulation, as well as regular posts from Peter.



  1. JC72 | | #1

    Very Kool ! ;)
    It's nice to see a product deliver on its claims.

  2. gusfhb | | #2

    'ow much does it cost
    'ow much does it cost

  3. Expert Member
    Peter Yost | | #3

    Kooltherm cost
    Kingspan claims pricing is competitive with foil-faced polyiso rigid foam insulation.

  4. GBA Editor
    Martin Holladay | | #4

    Online pricing in the U.K.
    Here is a link to a British website selling Kingspan Kooltherm:

    For a product described as "external wallboard insulation" measuring 50 mm (2 inches) thick, the price is £11.76 to £12.31 per square meter, depending on quantity. That translates to $16.82 to $17.60 per square meter, or $1.56 to $1.64 per square foot.

    For purposes of comparison, it's worth noting that in the United States, Home Depot sells 2-inch thick Rmax polyiso for $0.95 per square foot. Here is a link:

  5. Randy_Williams | | #5

    Do the thermal properties of
    Do the thermal properties of the insulation remain consistent as the insulation ages and is there any decrease in R-value when exposed to lower temperatures? Can the insulation also be used exterior?

  6. Expert Member
    ARMANDO COBO | | #6

    Roof assembly
    Is it right to install dense packed cellulose against the roof decking, specially on cold climate?
    "2015 IRC R806.5.1.3. Where both air-impermeable and air-permeable insulation are provided, the air-impermeable insulation shall be applied in direct contact with the underside of the structural roof sheathing in accordance with Item 5.1.1 and shall be in accordance with the R-values in Table R806.5 for condensation control. The air-permeable insulation shall be installed directly under the air-impermeable insulation."

  7. AlanB4 | | #7

    Hard to believe
    I would like even more testing and if true its mighty impressive.
    I would like to see (safe) longer term testing with the blowtorch, a few mins would be nice at both the edge and the face.
    I don't like proprietary, i want to know what i am buying, patented is okay since the patent is public knowledge.

  8. Expert Member
    RICHARD EVANS | | #8

    Foil Facing and R-Value
    According to the third party testing document (provided in this article), the actual R-Value per inch is 6.2 or 6.3 per inch. Does it become R8.2 per inch when the insulation board includes the foil facing? Without an air gap, I presume we have to bring the R-value down.

    Seems like a great product though. I too am curious to see how the R-Value changes with temperature and to what extent it is vapor permeable. I would also like to see how it compares to EPS or Polyiso from a Global Warming Potential perspective.

  9. GBA Editor
    Martin Holladay | | #9

    Response to Rick Evans
    You are quite right: the third-party report from Intertek shows an R-value of either R-6.2 or R-6.3 per inch for 1-inch-thick samples.

    For the time being, I have edited the article to reflect this report. I intend to follow up with Peter Yost in case there is more to the story than it currently appears..

  10. Expert Member
    Dana Dorsett | | #10

    The 1" samples are lower R/inch than the 3" @ Rick Evans
    The fiber-faced 75mm (2.95" ) samples (K20, K5 & K3) tested at R24.9 ( /2.95" = R8.44 per inch).

    The foil facers deliver LOWER R/inch.

    The foil faced 75mm samples (K15, K8, K7, & K12) tested at R23.8 ( /2.95" = R8.07 per inch)

    But the 25mm samples all test in the sixes.

    This suggests significant non-linearity in the R v.s. mean-temperature curve, a non-linearity that is probably relevant if used on the exterior side of the assembly, just as it is with most polyisocycanurate. A double-layer of the 30mm goods (60mm = 2.36") probably comes a bit less than the R8.07/inch of the 75mm foil faced samples, but it would be useful to see the curve plotted against temperature.

  11. gozags | | #11

    As Armondo mentioned...
    Is it proper to put the cellulose right to the underside sheathing in a cold climate? Would it have worked better to put damp/wet applied in place, cut it back to the rafters then do the foam?

  12. GBA Editor
    Martin Holladay | | #12

    Response to Armando and Sean
    The installation of dense-packed insulation in contact with the underside of the roof sheathing does appear to be a code violation, although it's worth pointing out that a local code official has broad authority to allow methods that appear to violate the letter of the code.

    I imagine that the homeowners and architect argued that slate roofing is vapor-permeable. Because of this fact, this code violation isn't as risky as it appears. The problem, of course, is that if the house is ever sold, the next owner of the home may decide to install asphalt shingles or a standing-seam roof. Once that happens, the risk of moisture accumulation in the roof sheathing (especially on the north side of the roof) increases significantly.

  13. GBA Editor
    Martin Holladay | | #13

    Kingspan responds to R-value questions
    I just received an email from Peter Yost, who forwarded the following response from Kingspan: "Kooltherm R-value is lower at 25mm [1 inch]. Everything we are selling in the U.S. is thicker than that and R-value increases substantially after 25mm."

    Intertek (a third-party lab) reports that the R-value at 75 mm (3 inches) is between R-7.93 and R-8.3 per inch, and I have no reason to doubt that report.


  14. AlanB4 | | #14

    Not buying that non linear R value improvement
    Polymers are made of repeating monomer units, tripling the thickness would triple the effect, not more, unless this is some kind of wonder material or has different properties when made thicker. If so make it thicker and trim thin to keep the higher R value at thinner values...

  15. Expert Member
    Michael Maines | | #15

    It seems plausible that the
    It seems plausible that the faces of the material would have more resin and fewer bubbles, or some other mechanical difference due to the manufacturing process, affecting the R-value for thin samples.

  16. AlanB4 | | #16

    Not convinced
    I'm still not convinced, and if true then make thick sheets and trim and sell the higher R versions in the thin iterations, there would be a market for "premium thin" insulation for those who are stuck with certain assemblies.
    Its not impossible for the data to be correct but one test from one lab giving hard to believe data is not easy to accept, they need to figure out why they get this result, replicate it elsewhere and prove this counter intuitive data. If its accurate it can be done.

  17. Expert Member
    RICHARD EVANS | | #17

    R-Value and Temperature @ Alan B
    Alan B, I don't think the insulation material in non-linear. Rather, it's performance (R- Value to Temperature) may be. Dana gave the example of poly-iso. Its R-Value decreases as the temperature drops. At zero degrees F, its R-value is probably around R2 or R3, per inch. But if you cover that Polyiso with another inch of polyiso, then the first inch of poly-iso is "warmed up" and will have a measurably higher R-value-(R4ish?

    With Kool Therm, the outer inches must be warming up the inner inches of foam- boosting overall R value for thicker sheets. This must mean however, that the the inner inch has a REALLY high R-value to bring the total up to 8.2 per inch.

    Is there a theoretical limit to R-value per inch? This inner layers must be around R-10/inch!!

  18. gusfhb | | #18

    Michael's thought seems plausible, in fact in thinking on it, one wonders why there isn't more variance in other materials, or perhaps they are only tested at one thickness

  19. gusfhb | | #19

    I do not believe polyiso is
    I do not believe polyiso is at R2, ever

  20. GBA Editor
    Martin Holladay | | #20

    R-value testing
    When a third-party lab tests an insulation material to determine its R-value, the test procedure is ASTM C518, "Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus." This is a material test to determine the R-value of an insulation material.

    The ASTM method requires testing at a mean temperature of 75°F, so cold-weather performance of polyiso is not an issue.

  21. Expert Member
    Michael Maines | | #21

    ASTM C518 allows testing at
    ASTM C518 allows testing at various thicknesses, up to 250mm (about 10"), as long as the testers don't think edge losses will affect the result. They can test at a single thickness or at multiple thicknesses and fit a smooth curve between the points. So different foam manufacturers can use different thicknesses of foam for their advertised R-value. I believe that most rigid foams perform best in thinner samples, presumably because the gas cells are tighter at the edges, but it sounds like Kooltherm was likely tested at a thicker sample, so the unusual edge effect would have less of an impact.

    It's certainly possible to have the faces of the material shaved down, but it adds to the material cost--it's much easier to take it straight from the die or mold.

  22. Jon_R | | #22

    A higher volume to surface
    A higher volume to surface area ratio means less gas escapes. So better R/inch in thicker versions. Similar with facing.

  23. AlanB4 | | #23

    "Is there a theoretical limit
    "Is there a theoretical limit to R-value per inch? This inner layers must be around R-10/inch!!"
    Thats even less believable

    Aerogel has an incredible R rating per inch, but its well tested, researched, explainable and proven (and very expensive and fragile).

  24. GBA Editor
    Martin Holladay | | #24

    A correction
    Michael Maines just emailed me, pointing out that testing insulation at a mean temperature of 75 degree F is not a requirement of ASTM C518. Michael is right. I stand corrected.

    The reason that U.S. insulation manufacturers test at a mean temperature of 75 degrees F has nothing to do with ASTM C518. It is due to the fact that federal law makes it illegal to sell insulation labeled with R-values determined at a mean temperature other than 75 degrees F. The relevant statute is the Federal R-Value Rule (16 CFR Part 460, “Trade Regulation Rule Concerning the Labeling and Advertising of Home Insulation”). Here is a link to the relevant section:

    Here are the relevant paragraphs:

    “460.5 R-value tests. … R-values given in labels, fact sheets, ads, or other promotional materials must be based on tests done under the methods listed below. They were designed by the American Society of Testing and Materials (ASTM). The test methods are:
    (a) All types of insulation except aluminum foil must be tested with ASTM C 177-04, “Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus;” ASTM C 518-04, “Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus;” ASTM C 1363-97, “Standard Test Method for the Thermal Performance of Building Assemblies by Means of a Hot Box Apparatus” or ASTM C 1114-00, “Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus.” The tests must be done at a mean temperature of 75 [degrees] Fahrenheit and with a temperature differential of 50 [degrees] Fahrenheit plus or minus 10 degrees Fahrenheit. The tests must be done on the insulation material alone (excluding any airspace). R-values (“thermal resistance”) based upon heat flux measurements according to ASTM C 177-04 or ASTM C 518-04 must be reported only in accordance with the requirements and restrictions of ASTM C 1045-01, ‘Standard Practice for Calculating Thermal Transmission Properties from Steady-State Conditions.’ ”

    Since this is a federal law, this is how American manufacturers test and report their R-values.

    In the back of my mind, I know the source of this regulation, but somehow I referred to ASTM C518 instead of the R-value Rule. Thanks, Michael, for setting me straight.

  25. user-2069108 | | #25

    Fire resistance
    Although the insulatio values are difficult to believe, I would like to address the fire resistance. Is it any better than other foil-faced polyiso foam? We all know the EPS and XPS are very flammable (just toss a piece on an open fire), but my very empirical test of polyiso form on the same fire only resulter in veey short period of flame, but that was only after being poked with a stick. Otherwise, I would suspect that it would have just sat there barely smoldering. In another incident, I know of a parked flatbed truck loaded with the foam being struct with lightening. Once again, it did not ignite. It did smolder, though.

  26. AlanB4 | | #26

    @ Steve
    Thats a good point, i remember someone giving a demonstration of nanotherm (or insulate, whatever its called), and it consisted of a hot pot of water, half the side was covered with the nano(whatever) and half was bare metal and voila the covered half was not as hot (but still warm).
    It was an effective if misleading demonstration, zero R of metal vs 0.25ishR of the product. There was no comparison to other coverings and any 0.25ishR equivalent covering would have performed exactly the same (some plastic or regular paint would probably do the job).
    One of those miracle sponges on TV would go on about how it absorbed (X) times its weight in water. Exactly the same as any other sponge but they neglected to mention that part.

  27. Expert Member
    Peter Yost | | #27

    does this roof assembly comply with code?
    There is a long answer to this, which I will probably do in a separate blog--since how most recent codes treat roof assemblies is complex and inadequate from a building science perspective--but the short answer is yes: the current VT code, in the section for existing homes states (4.1.8): "Roofs without insulation in the cavity and where the sheathing or insulation is exposed during reroofing must be insulated either above or below the sheathing." This roof assembly complies.

    Suggesting that unvented roof assemblies cannot or should not be designed to dry to the exterior is like suggesting that unvented wall assemblies can not or should not be designed to dry to the interior. If you manage wintertime condensation with an interior air barrier and interior vapor retarder along with drying to the exterior, that is high performance to me.

  28. GBA Editor
    Martin Holladay | | #28

    Response to Peter Yost
    Thanks for sharing that section of the code. However, I disagree with your conclusion. Just because the code requires that the contractor must install insulation either above or below the sheathing, doesn't mean that the contractor gets to install the insulation in a way that violates other sections of the code.

    Here is a quote from the Vermont Energy Code Handbook:

    "Unvented attic assemblies (spaces between the ceiling joists of the top story and the roof rafters) are permitted in one- and two-family homes and multiple single-family dwellings (townhouses) if all the following conditions are met: ...
    "2. Air-permeable (e.g., fiberglass or cellulose) insulation only. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board sheet insulation must be installed directly above the structural roof sheathing as specified in Table R402.4.1.1 for condensation control.
    "3. Air-impermeable and air-permeable insulation. The air-impermeable (e.g., spray foam) insulation must be applied in direct contact with the underside of the structural roof sheathing as specified in Table R402.4.1.1 for condensation control. The air-permeable (e.g., fiberglass or cellulose) insulation must be installed directly under the air-impermeable (e.g., spray foam) insulation."

    In the 2015 Vermont Residential Building Energy Standards, the relevant requirements are listed in section 402.2.2.1. Here is the link (scroll down to see the section I'm talking about): 2015 Vermont Residential Building Energy Standards section 402.2.2.1.

  29. Expert Member
    ARMANDO COBO | | #29

    Roof assembly
    I could live with the fact that a wall assembly can be designed to dry to the outside, and if as Joe says, a roof assembly is a wall assembly on an angle, why can a roof assebly dry to the outside, right?. Slate roof over bldg paper and sheathing are permeable, and the layers of taped and seal rigid foam wont let any interior moisture to the sheathing and outside, so it makes sense... but, has any research been done to show this assembly can work? I do look forward to your next blog. Thanks.

  30. GBA Editor
    Martin Holladay | | #30

    Response to Armando Cobo
    As I noted already in Comment #12, the argument can certainly be made that this roof assembly can dry to the exterior because the existing roofing is slate. The problem is that roofing is often replaced by homeowners, and new roofing (for example, asphalt shingles or standing-seam metal roofing, both of which are far more common in Vermont than slate) would immediately put the roof sheathing at risk, especially on the north side of the roof.

    Maybe this roof needs several stainless-steel warning plaques, installed at the ridge and eaves, noting: "Warning! Roofers of the future! If this slate roofing is ever replaced with asphalt shingles, standing-seam metal roofing, or any type of vapor-impermeable roofing, this unvented cellulose-insulated roof assembly will accumulate moisture and fail!"

  31. Expert Member
    ARMANDO COBO | | #31

    Good points... I love the WARNING! signs idea... LOL

  32. AlanB4 | | #32

    Warning signs
    Indeed, i remember reading about the idea of houses coming with instruction manuals, if tailored to the house its a great plan. How to convince future owners to update what they have changed, not sure.

  33. Expert Member
    Peter Yost | | #33

    Harping on exterior cladding changes vs. interior wall finishes
    Really, we are worried about the impact on drying potential when exterior claddings change when any building assembly designed to dry to the interior can change whenever a homeowner decides to change interior finish?

    Very few of our high performance assemblies will not need high performance re-evaluation/supervision when either the exterior claddings or interior finishes are altered.

  34. Expert Member
    Peter Yost | | #34

    Conflicts built into the code
    I respect your disagreement Martin, but frankly complying with both sections of the code would come down to the local building inspector reconciling. And for sure this is not the only instance when the code got the building science wrong or had incomplete and/or conflicting language in different sections.

  35. GBA Editor
    Martin Holladay | | #35

    Response to Peter Yost
    The title of your recent comment is "Conflicts built into the code," but I see no conflict.

    The code you cited informs roofers that if sheathing or existing insulation is exposed in their reroofing work, the roofers must install insulation either below the sheathing or above the sheathing.

    In the house described in this blog, there was no reroofing, so the code section you cite doesn't apply. According to your Comment #27, this section of the code only applies to projects "where the sheathing or insulation is exposed during reroofing."

    Furthermore, even if this were a reroofing job -- it wasn't -- a roofer could comply with the cited code provision by installing rigid foam above the roof sheathing or spray foam below the roof sheathing. I have no idea why you think that this code section compels anyone to install dense-packed cellulose against the underside of the roof sheathing. It doesn't.

  36. Expert Member
    Dana Dorsett | | #36

    Yes, polyiso can perform at R2/inch @ Keith Gustafson
    Take a look at this graph:

    When the mean temperature (not the cold side temperature) through the foam is about -20C /-4F the conductivity of the foam is about 0.073W/mK or a bit over 0.5 BTU in /(hr ft2 F), which at 1" would be an R value of 1"/(0.5 BTU in /(hr ft2 F) ). The fact that it's a bit over 0.5 BTU in /(hr ft2 F) means it's actually a bit less than R2.

    So, in your comfy-cozy 70F house when it's -78F outside, if polyiso is the only insulation layer that foam is really only doing ~R2/inch.

    If it's an exterior sheathing application and the warm side of the polyiso is +25F, it hits R2/inch at "only" a toasty -30F outside.

    For most of us, in most stackups, even at the 99% outside design temperature polyiso will be performing well above R2/inch. And the seasonal average will be higher still.

    Looking at Karagiozis' curve it appears that his sample hit ~R6.7 at about 16C /61F through the foam, but only about R5.8 at the FTC mandated labeling test temperature (the blue vertical dotted line), which means it was almost certainly 2lb roofing foam, not the lighter higher-R foil faced stuff, so MAYBE 1lb foil faced polyiso won't quite make it all the way down to R2/inch @ -20C mean temp, but it'll be close.

    Dow claims to have solved & fixed the polyiso derating puzzle with Thermax, but they don't share their proprietary solution, only the results:

  37. MKCF | | #37

    I've been waiting to get my hands on some of this stuff since August. The sales rep has been about the least useful person I've ever encountered. When is phenolic board insulation going to become readily available?
    As a side note, here in CT there is a company that does spray foam phenolic. Not sure where that falls compared to Kingspan in terms of performance. but I can say it sure is expensive.

    1. Sofiane | | #44

      Did you have any luck buying it? I tried to obtain information on availability in Canada and cannot even get an answer so far.

      1. this_page_left_blank | | #45

        This seems like a company that will disappear from this market in pretty short order. Or maybe they will linger for a long time, but without actually moving any product during that time. If they started offering the stuff in the US in 2016, and three years later they don't have any discernible way for customers to buy it, and their sales people aren't interested in talking to potential customers (isn't that their job?), then they are a catastrophe.

        1. brendanalbano | | #46

          They also might not focus on the scale of work most of us discuss on this website. If I'm remembering correctly, I went to a presentation about the new Multnomah County Courthouse ( ) and they are using insulated panels manufactured by Kingspan.

  38. lutro | | #38

    Code compliance confusion, comment #28, etc
    The wording in the quoted sections of the building code don’t paint a complete and unambiguous picture for me. Peter quotes a section stating that roofs "must be insulated either above or below the sheathing.” I’m guessing that this sentence is interpreted as “and/or”, rather than an exclusive “or”. That is, the insulation can be above AND/OR below the sheathing, rather than prohibiting any/every combination of interior and exterior insulation. I’m supposing the “and/or” interpretation, because a combination of exterior and interior insulation seems to be specified/required in paragraph 2 of Martin’s quote of the building code in comment #28.

    Here is a portion of the code that Martin quotes. ""2. Air-permeable (e.g., fiberglass or cellulose) insulation only. In addition to the air-permeable insulation installed directly below the structural sheathing, rigid board sheet insulation must be installed directly above the structural roof sheathing as specified in Table R402.4.1.1 for condensation control.” As I read it, this item REQUIRES a combination of interior and exterior insulation in this configuration, whereas that would be prohibited if the “or” in Peter’s quote was an exclusive “or”.

    The 2015 IRC IRC R806.5.1.3. code language quoted by Armando Cobo in comment 6 seems to prohibit the roofing configuration insulation scheme described by the architect/builder Eli Gould, as quoted by Peter. The "as built" description also seems in conflict with paragraph 3 of the code section quoted by Martin in comment #28.

  39. GBA Editor
    Martin Holladay | | #39

    Response to Derek Roff
    The section of the code quoted by Peter Yost is irrelevant to this project. The code section he quoted only applies to re-roofing jobs. This was not a re-roofing job. The slate is still there.

  40. gusfhb | | #40

    re Dana
    Not trying to push the point here, but, generally we are talking about buildings below the arctic circle, so yeah, 2 is pushing it. Also that particular graph seems to go further than other graphs on this website, even conflict.

    still haven't seen a US cost on this material

    It might be interesting since it need not be covered.

  41. jaccen | | #41

    RE Reintroduction
    Of note may be why this product was previously discouraged in its use:

    "Phenolic foam insulation was manufactured and sold into the North American market in the 1980’s
    and early 90’s, mainly as roofing insulation. Claimed benefits were high insulation value and excellent fire resistance. High moisture absorption potential and residual acid present in the foam allegedly resulted in significant corrosion issues. Class action lawsuits were filed against corporations in the early 1990’s. Past litigation in North America focused on corrosion allegedly caused by phenolic foam used in metal deck roofing applications. The resultant roofing failures and subsequent litigation are still fresh in the minds of the building community. "

    Installation on the exterior or in high humidity areas (ie. bathroom) may require consulting the manufacturer of whether it is advised or not.

  42. escyukon | | #42

    Anyone seeing anything on availability of this product in North America? I don't see much on the web.

  43. therealcactus | | #43

    usable in basement?
    this product seems to be more similar to polyiso rather than eps or xps in terms of moisture absorption. can the foil faced phenolic product be used as a drop in replacement for polyiso on the interior side of an exterior concrete basement wall, followed by an empty stud wall and drywall?

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