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Community and Q&A

Polyiso Losing R-Value in Cold Climates

EfficiencyDude | Posted in Green Products and Materials on

GBA has written articles about polyiso losing insulation value as the blowing agents condense:

2015 article:

Owens Corning put out a bulletin about it the same year:

But now in 2022, I’m finding datasheets such as this polyiso from Kingspan, where they measure it from an extreme temperature range and it stays constant from -50f to +75f:

Similarly, they claim the polyiso and the proprietary Quadcore foam they use in their insulated metal panels, increases when the temp drops from 75f to 35f (check the R-Value tab):

My question is: are these values legit? Should the old articles be updated with this new info? Or is Kingspan using some trickery to get those cold performance values?

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  1. Expert Member
    PETER G ENGLE PE | | #1

    Numbers are probably legit. All of the earlier test data I've seen reported noted that there was a wide variation in performance between manufacturers. Also, since the blowing agents are proprietary, it was difficult to tell how much of the R-value variation with temperature was related to the blowing agents and how much to the nature of polyiso. Tests did find some samples of polyiso that showed little effect of cold weather on R-value. So Kingspan has come up with a blowing agent that resists the cold weather effects. Not surprising since R-value loss in cold weather has been one of the primary criticisms of polyiso.

    My primary concern with the specific product you posted is that it is a very high density, rigid product that is designed for very wide temperature ranges. It will probably work fine in a residential setting, but is likely to cost several multiples of what a more standard product would be. And, it looks like it is custom formulated and/or fabricated for each customer, so availability could be severely limited. But check out their other weight products and you might find a residential panel with low R-value variation that uses the same blowing agents.

  2. Expert Member
    BILL WICHERS | | #2

    There is nothing about polyiso that requires that it always reduce in R value in cold temperatures. It's not the polyiso itself that has that property, it's the blowing agents used in it's manufacture. Early (1980s) vintage polyiso didn't show this "looses R value when it's cold" issue. What happened was that the blowing agents were changed in the 90s due to restrictions on some HFC compounds, for simialr reasons to why certain refrigerants like R12 were phased out. The newer blowing agents showed the "reduced R value in the cold" problem, but to varying degrees.

    Dow Thermax, for example, has long claimed better cold weather performance compared to other variants of polyiso. Manufacturers are aware that customers would prefer that the R value stay constant or increase with falling temperatures, so there is some incentive for manufacturers to improve their products. Kingspan is probably using a different blowing agent that has better cold weather performance, and they're hoping to use that as an edge over their competition. I have no reason to doubt their numbers, aside from that they may be trying to show things under optimal conditions for their product (meaning it might not always quite live up to their claims under real world conditions, but it's probably still better than other products on the market). I doubt very much that their numbers are pure fabrication.


  3. GBA Editor
    Kiley Jacques | | #3

    Hi EfficiencyDude,

    Your question made me wonder if we did, indeed, need to update the information we have on the topic. I asked Scott Gibson to research whether a refresh was in order. As always, he jumped right on it and has this to share:

    The R-values of these two Kingspan products may be perfectly legit, but they don’t have much to do with the polyisocyanurate insulation installed on walls and roofs in residential construction.

    First, Kingspan doesn’t manufacture polyiso for the U.S. market. That’s according to both a Kingspan marketing manager and the Polyisocyanurate Insulation Manufacturers Association (PIMA). The “QuadCore” insulation in the Optimo Wall Panel is described by Kingspan as a “hybrid” rated at R-8 per inch. Kingspan says that’s 11% better than even high-quality polyiso. Although Kingspan didn’t answer emails asking for more information, let’s assume that “QuadCore” is not polyiso. Also, the Optimo panels are for use in cold storage, commercial and industrial applications. It’s not for houses.

    The Kingspan ISO-C1 insulation you mention is polyiso, but it’s manufactured in large blocks called “buns” that are turned into insulation for a variety of commercial and industrial uses—panels, pipe insulation, and equipment insulation. It’s not the board stock you buy at Home Depot. This product is apparently made by Dyplast, a company acquired by Kingspan last year.

    What about the polyiso industry as a whole? Traditional polyisocyanurate formulations still have the same cold-weather issues disclosed in tests by the National Roofing Contractors Association and the Building Science Corp., and reported at GBA. In a nutshell, R-values decline as the temperature falls. Part of the problem may be related to the pentane or a pentane blend blowing agents that manufacturers have used. They still dominate the market.

    The NRCA recommended in 2016 that designers use an in-service R-value of 5.0 per inch for polyiso roofing assemblies. And that advice hasn’t changed.

    But the industry has been working on the problem, with some companies further along than others. Firestone, for example, promotes “ISOGARD” on its website with claims that its thermal performance is significantly better than competitors (more than R-6 at a mean temperature of 40° F). Trouble is, you can’t run down to the lumberyard and buy this polyiso in board stock, either. Firestone is not a player in the residential market but concentrates instead on large scale commercial work.

    Kohta Ueno of Building Science Corp. reminds us that not all polyiso insulation behaves in exactly the same way. BSC’s 2013 research shows that the R-value of some products remained over R-5.5 for the entire temperature range (mean temperatures from 25° to 75°). PIMA adds that it’s misleading to suggest that polyiso simply stops working when it gets cold. In a roof assembly with 6 in. of insulation, for instance, the bottom inch of the insulation is behaving differently than the outermost part of the assembly because the mean temperatures are different depending on where they are measured. Builders may want black-and-white answers but the situation is more nuanced than that.

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