Open Cell Vs Closed Cell Foam Insulation

By Todd Fratzel on Insulation

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

About the author

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the author of Tool Box Buzz and Today's Green Construction. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

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  1. 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?

    • Todd says:

      Matt – I would always use closed cell foam. IMHO open cell should really never be used.

      • Matt says:

        Thanks Todd

        • Brian says:

          Did you mean that you would “Only” use closed cell foam, or Only use closed cell foam when dealing with moisture?

          also, is this correct:
          Expanded polystyrene foam (EPS)is open cell foam
          Extruded polystyrene foam (XPS)is open cell foam
          Polyisocyanurate is closed cell foam


          • Todd says:

            I try to avoid open cell foam altogether to be honest. If you ever get a leak it acts like a sponge. I’ve seen far too many situations where open cell foam turned into a nightmare because it holds water.

            EPS – Open Cell
            XPS – Closed Cell
            Polyiso – Closed Cell

  2. 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).


    • Todd says:

      Michael – The R values will depend on the manufacturer and thickness.

      There is no standard based on the price of a home.

      You would need to create an accurate energy model for the home to come up with those numbers.

  3. 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.



  4. 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.

  5. 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?

  6. Tee says:

    We’re starting construction on our basement in the next few days. I want to make sure the construction company uses the right type of insulation and doesn’t try to “go cheap” or use the wrong thing. So I’ve learned here that we should use closed cell. What R value is best? Also, can you recommend a few manufacturer’s names for quality closed cell insulation with good R value?

    Thanks for your advice.

  7. Kurstin says:

    Hi! My husband and I have heard conflicting views on foam insulation as well. we are building a home on a custom built flat bed trailer. It’s 6in deep. We were considering closed cell but were worried about the remaining 3in air gap. And which would be better: spray foam boards or having a company spray it? Also, we weren’t sure if closed or open would be a better bet. Any and all advice appreciated.


    • Todd Fratzel says:

      Kurstin – I only recommend closed cell foam. Open cell foam can absorb water and that’s a bad thing! Spray foam is always better than sheets, but it comes at a price. Good luck.

  8. 20 units of a Gatlinburg, TN complex have bathroom copper water lines in contact with the 8″ block outside wall. With mid-teens temp for an extended time-the lines will freeze and rupture. I am
    assigned to find an “economical” solution. I proposed using 2″
    closed cell foam board with Hardy cement stucco covering the foam
    and trimmed with wood for esthetics. In your opinion, am I wasting
    time and money with this fix?

    • Todd Fratzel says:

      Gary – The 2″ foam should work well. You lost me on the Hardi board…is that a finished exposed surface? Just curious.

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