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Polyiso foam insulation densities

Salesi | Posted in General Questions on

Are there any differences in densities of polyiso foam board insulation? I see the product at the home centers and then see a product by Dow Tuff R Commercial polyiso insulation board. Just like EPS has a high density insulation board, does polyiso have the same thing? I am in zone 5 and plan to use polyiso on the exterior of my house with all the joints tapes and a rain screen on top of the board.

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  1. Expert Member
    Michael Maines | | #1

    Salesi, yes, all types of rigid foam are available in different densities. For use on a wall, any available density of polyiso will work, though the more dense the less it will compress when you install the battens, and the R-value is probably slightly higher as well.

  2. Salesi | | #2

    Michael: Thanks for the response. Typically the polyiso foam boards at the big box stores seem pretty fragile to me anyways. I have been looking for a source for denser polyiso but have not been able to locate a supplier.

    1. Expert Member
      Michael Maines | | #3

      Salesi, one rule I've learned repeatedly is to never try to special order anything at a big box store. If you want to buy new foam, I would go to a real lumberyard or a roofing supplier. Standard compression resistance (often called "density," though that's not quite accurate) is 20 psi, but 25 psi or higher polyiso is available. Even better, find a source for used/recycled foam, as all foam has a significant carbon footprint, with upfront carbon emissions that contribute to the climate crisis. Recycled foam is usually from commercial roofs and is likely 25 psi or higher. Just be aware that because polyiso shrinks as it ages, the thickness may vary from sheet to sheet.

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