Open Cell Vs Closed Cell Foam Insulation

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Open Cell Vs Closed Cell Foam

Spray Foam Insulation 201x300 Open Cell Vs Closed Cell Foam InsulationIt seems quite a few readers have questions about the difference between open cell and closed cell foam insulation.Understanding the difference between open cell and closed cell foam insulation is the most important step in determining which product is best for your next insulation project.

Foam Insulation Porosity – Vapor Barrier Issue

Open Cell Foam Insulation is a porous material that can allow air and moisture to penetrate the insulation. Closed Cell Foam Insulation is non-porous with all of the voids closed to each other which makes it difficult for water vapor and air to pass through it. The porosity of the two materials is the biggest difference and most important issue. If your insulation application needs a vapor barrier then you MUST select closed cell foam insulation.

Foam Insulation Density – Cost & Strength Issue

The other major difference between open cell and closed cell foam insulation is the density of the in-place foam.  Open cell foams typically weigh about 0.5 lbs per cubic foot while closed cell foams are about 3 lbs per cubic foot. Ultimately this is why closed cell foams are stronger and denser allowing them to carry heavier loads. This is also one of the reasons that closed cell foam is quite a bit more expensive compared to open cell foam.

Insulating Value – R Values Per Inch

The final issue when discussing the differences between open cell and closed cell foam insulation is the insulating value or R value per inch of insulation. Open cell foam insulation typically has average R values of about 3.5 per inch while closed cell foam insulation has average R values of about 6.5. So you can see closed cell foam insulation can be almost twice the insulating values per inch.

Photo Credit: Elizabeth Buie

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  • Matt says:

    I understand that I should use closed cell in my below grade poured concrete basement walls due to moisture, but what about the above grade rim joist and the above grade wall in the walk out part of the basement? Could you use closed cell or do these parts of a wall need to let moisture vapor pass through?

  • Michael Michael says:

    So I can compare better, can you please tell me what the “R” values are of the products below:

    > Closed cell foam
    > Open cell foam
    > Typical standard insulation in a $250K home
    > Typical high end insulation in a $500K home

    I see R values for Open / Closed, but can’t compare all of the different insulation types.

    Last question, for each R value increase, how much energy / utilities does that save a home owner on a typical home (say 2,000 square feet).


  • David White says:

    Hello Todd, I was very upset when I read these forums and it was brought up that EPS is open celled, due to the fact that I completed 90% of my basement insulation with this product. I did some research and EPS is supposedly closed cell phone according to everyone else. Which is it?

    And if it is closed cell, do you think I will have future problems? I have a newly built poured concrete basement. The 2″ EPS has a foil facing on it and plastic facing on the other side. Thanks very much..This website has helped me with alot of projects…and has very good information. I cant wait to do the attic hatch!! :)


    • Todd says:

      David – Are you 100% sure you used EPS? Typically the foil faced foams are either XPS or Polyiso. The confusion comes from the pure definition of EPS which includes closed cell foam balls. The balls of foam are indeed a closed cell foam. However, the structure between balls is NOT. Depending on the brand and manufacturing the porosity of EPS foam can be quite high which makes it in effect an open cell foam.

      “Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam. It is usually white and made of pre-expanded polystyrene beads.”

      EPS-Foam Company:
      “EPS foam by its nature is mostly air, and depending on the density of the foam, there will be more or less air between the fused closed cell beads of EPS. The higher the density, the more beads and consequently the less space for air between the beads.

      There is some confusion between water absorption with EPS foam and fusion of the beads. Because of the porosity of the foam, the water absorption is a product of how much air or space there is between the closed cell beads of EPS. It is therefore possible to have foam that has low water absorption and poor fusion, which makes for a poor quality product for use as a surfboard or paddleboard product.”

      Make sense?

      • David White says:

        Thanks for the quick reply. I will check when I get home and will send you a picture.

        All aside , tho I have 90% completed, and have not even started on the rim joists yet…I had a increase of 6 degrees F so far….my nonheated basement stays a firm 60 degrees F even with drastic temperature changes.



  • MIKE says:

    Hello Todd my question is this i’m building a metal home and want to use spray foam insulstion and i’m getting some confusing info on the difference between open cell and closed cell foam. One company i spoke with says to use open cell on the ceiling and walls, another co. says to use 2″ closed cell on the ceiling and 4″ open cell on the walls. please help!!!!

    • Todd says:

      Mike – Metal buildings can be different that wood constructed ones. However, metal buildings are typically commercial buildings which have far better HVAC systems in place to deal with humidity.

      What type of framing?siding? finishes are you using? Without that information it’s difficult at best to pass judgement.

  • Alicia says:

    Hi Todd. I’m reading all of the information everywhere about the closed vs open foam. Everywhere has said use the closed if you can afford it. We have a 40yr old home in Southwest Louisiana. It’s hot! 95degree days, 80/90% humidity. I recently had a bid to spray the attic, vents….and decided on the closed cell. BUT, when our A/C fan motor went out and I called our A/C guy, we talked about the two options and he said I wanted open cell NOT closed! I’m so confused. Can you shed any light on the matter?

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