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Community and Q&A

Roxul Comfort Board vs. Thermafiber RainBarrier

Caitanya Joy | Posted in Green Products and Materials on

Any differences I should be aware of before I choose? I am wanting to use mineral wool for exterior insulation on a wood frame, two-story dwelling. Very impressed with Roxul online information, technical specs etc. Can’t find much about RainBarrier, other than the company info sheet, but it’s 1/2 the price of the Roxul. Thermafiber says that the Rainbarrier HD is the product they have made to be comparable to Comfort Board, but cannot find any comparisons between the two.

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  1. John Semmelhack | | #1

    What kind of price quotes are you getting? I would be very surprised at a 50% price difference for an apples to apples product.

    You might also want to get pricing on Roxul Rockboard 80, which is (from what I can tell + talking with a rep at a trade show) more or less the same product as Comfort Board IS, but is generally lower priced ("different distribution channels" is the pat answer that I get). Folks here in Virginia have been getting Rockboard 80 at roughly $0.40/ft2.inch.

  2. D Dorsett | | #2

    RainBarrier is 6lbs per cubic foot, R4.2 per inch, and can be had in thicknesses up to 7" (!).

    ComfortBoard IS is 8lbs per cubic foot and R4.0/inch, but somewhat less air permeable.

    Both are pretty good products- if you can get RainBarrier for half the price of ComfortBoard, it's hard to make a case for going with the more expensive higher density but slightly lower-R product. I suspect the higher density goods are a bit more rigid, but at 6lbs density it won't exactly be floppy. The ComfortBoard CIS is 11lbs density which is probably noticeably stiffer (though I can't say I've compared them side by side.)

  3. Robert Hronek | | #3

    What affect does air flow in a rainscreen wall affect the performance?

  4. D Dorsett | | #4

    At these densities (more than 2x high-density batt densities) thermal performance is not affected by the lack of a true air-barrier. With direct wind washing and high wind it might be. At the air flow rates in a rainscreen gap it is probably not measurable.

  5. Brad Hardie | | #5

    If you are hoping to use Thermafiber for a PERSIST type exterior insulation installation, be weary that the compressive strength of Thermafiber Rainbarrier 45 is 67psf @ 10% and 185psf @ 25%. The Rainbarrier HD is 76psf @ 10% and 256psf @ 25%. Comfortboard IS density is 8.0/lbs cu ft and is nearly over 10 times the compressive strength of Rainbarrier. Comfortboard IS @ 10% is 745psf & at 25% is 1270psf. This considerable. According to Thermafiber Tech support you would need a stand-off or sleeve to hold off the compression. With the Roxul you do not. Building Science Corporation has done studies on the use of Roxul on the exterior to test if there is vertical shift and to see if the Comfortboard IS compresses too much. Good stuff.....

  6. Caitanya Joy | | #6

    Thank you for the responses. After quite a bit of consideration we are going to use FoamGlas on the exterior stem wall and are changing the system to have a higher interior R-value allowing for more flexibility on exterior insulation. We came across the same density problems with Thermafiber and ended up moving away from it for this reason. Roxul is a great product, but the wait time is 8 weeks and the price is just so high. FWIW we called a Virgina Beach Home Depot for a Roxul quote and found that it was about 44% cheaper to purchase from Virginia and have it shipped to an Oregon store. We were completely honest about what we were doing and the guy said it was fine and he was uncertain as to the price difference. He said it was a newer product for them and that may be why? Thanks for all your help!

  7. Brad Hardie | | #7


    Be weary of the ratio of insulation on on the interior to the exterior. Before finalizing your decision, search for on discussions and articles on that here, and at Building Science Corp.. There is an optimal ratio basis on climate location (zone) to reduce/prevent moisture problems at the sheathing and inside the wall cavity.

    Dana Dorsett, Martin both have excellent understandings of this.

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