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Community and Q&A

Owens-Corning mineral wool compared to Roxul Comfortboard?

mathiasx | Posted in Green Products and Materials on


I’ve noticed that our local building supply store carries Owens-Corning R-16.8 “Safing Fire-Stopping Mineral Wool Insulation”. At a 4″ thickness, that’s something like R-4.2/inch.

In comparison, Roxul Comfortboard 80 R-6 48-sq ft Unfaced Rock Wool Batt Insulation with Sound Barrier (24-in W x 48-in L) (This is their 1.5″ thick Comfortboard) is R-4 per inch.

My guess is that the Owens-Corning product is less rigid and handles more like a fiberglass bat. Paradoxically, I’d think a “bat” is less rigid than a “board” but not having seen the Owens-Corning product, I am not sure. It may not be a good candidate for exterior “rigid” foam sheet style installation if it is indeed more like a fiberglass bat.

Has anyone used the Owens-Corning product as exterior insulation? How does it compare?



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  1. Expert Member

    I think you are comparing apples and oranges. Roxul also sells batt insulation which is very similar to the Owens-Corning you mention. They are both for filling wall or ceiling cavities. Neither are candidates for exterior insulation. Comfortboard is closer to rigid foam in it's applications.

  2. charlie_sullivan | | #2

    Malcolm, the material Matt is referring to is made by the thermfiber division of Owens Corning, not the fiberglass insulation division.

    Thermafiber makes mineral wool batts, and also makes a wide variety of mineral wool boards. The "safing" materials are boards and are available in 4 lb/cu ft or 6 lb/cu ft. Roxul Comfortboard 80 is 8 pounds per cubic foot. (80 pounds per 10 cu ft?). A closer equivalent to Comfortboard 80 is Thermafiber's "Versaboard 80" which is also 80 pounds per cu ft. They also have a water-repellent coated board for rainscreen use, called "RainBarrier" in 4.5 or 6 lb/cu ft.

    I see the safing material available at online stores like Menards. That's a specially fire-rated product. I would assume that a general purpose board would at least have a list price lower than that product. But I see no reason you couldn't use the safing board if the 25% lower density doesn't worry you.

  3. Expert Member

    Thanks Charlie,
    I stand corrected.

  4. GBA Editor
    Martin Holladay | | #4

    As Charlie implies, the key metric here is density. There are lots of articles on GBA discussing the question of the ideal density for exterior mineral wool.

    In one of my articles ("Installing Mineral Wool Insulation Over Exterior Wall Sheathing"), I quote building scientist John Straube, who told me, “The 6-pound-per-cubic-foot (pcf) and even the 4 pcf products did amazingly well, but the 8 pcf product was easier to handle for people used to the stiffness of foam and it also worked the best.”

  5. mathiasx | | #5

    Thank you for all the answers and for helping me understand this material!

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