Spray Foam R Values | Closed Cell & Open Cell Foam

December 4, 2009 | by Fred (email) |

closed-cell-spray-foamLast month we selected closed cell spray foam for the basement finishing project we’re working. Closed cell spray foam has the advantage of not requiring a vapor moisture barrier, and it also sports a very high R value, making it an ideal choice for insulating basements (and first and second floors alike).

A frequent question many homeowners ask is how much R value do different spray foams provide? We think that’s an excellent question, and the answer is, like R-values for rigid foam boards, it depends.

Open Cell Foam Insulation Values – R3 – R4

Open cell spray foams are between .5 and 1 lbs per cubic foot, and have an R value of 3.0 – 4.0 per inch of insulation. R values are additive, so you can multiple the number of inches of insulation thickness times the R value to arrive at a total insulation value.

A typical 2×4 stud filled with open cell spray foam will have an R value between 10.5 and 14. This R value is similar to that of R13 fiberglass batting; however, fiberglass generally does not provide as tight a seal as a foam product would, since it is unable to achieve as tight of a seal.

Open cell foam is relatively easy to cut, which allows installers to fill the cavity passed the edge of the studs and to cut off the excess.  This can’t be done with closed cell foams, but they require much less thickness to provide the same R value.

Common Applications: Open cell foam is generally used above grade in walls and sometimes in attics. Some open cell foams have restrictions on the spray height (limited to 5-6″ maximum in a horizontal installation).

Price: More than R13 fiberglass; less than closed cell foam.  Expect to pay about $1.25 for the first board foot in a room, and $0.80 for each additional board foot, depending on installation size.

Closed Cell Foam – R6 – R8

Closed cell spray foams are between 2 and 4 lbs. per cubic foot. They sport an R value of 6.0-8.0 per inch of insulation, about double their open cell foam counterparts.  Just like for open cell foam, R-values are additive.

Two inches of closed cell foam will provide R12 – R14 of insulation. Three inches will get you over R20, more than sufficient for exterior walls even the coldest climates in the United States.

Common Applications: Closed Cell Foam can be used throughout an entire house. It has the advantage of forming its own vapor barrier, and it can be sprayed to any thickness. The only drawback of closed cell foam is the price.

Price: More than open cell foam; one of the most expensive insulation options.  But, doesn’t require a separate vapor barrier. Expect to pay $1.75 for the first board foot in a room and $1.25 for each additional board foot.

Check with a Spray Foam Installer – R Values Vary

Before you commit to a spray foam installation, check with your installer to confirm the R value of the product.  Since R values can vary from manufacturer to manufacturer, and based on the chemical make-up of the foam, it’s important to understand the specific foam you’ll be installing.

What do you think? Will you install foam in your house?

13 Responses
  1. Connie B. says:

    Question, our builder told us that, using open cell foam, after the first 3 inches of open cell foam the R-value does NOT increase. Basically, the R-value would stay the same whether you used 3 inches or 6. Is that true? We have 2×6 exterior walls and 2×4 interior, he told me that the R value is the same regardless of how much they used…I think he’s trying to save $$ by not filling the 2×6 fully. Please clarify this for me. Thanks

    • Brian says:

      The r value does not stay the same, but its pointless to add more foam because after you hit 3″ there is virtually no air leakage. Adding more foam is a waste of money. At 3″ you will not need to turn on your HVAC system that much and virtually no air will escape. We’ve had to pump air in, its been so air tight.

  2. Jeff says:

    I stumbled across your blog looking for info on closed cell spray foam insulation. I’m also looking to insulate my basement, and in all my reading, I haven’t heard anything about something you stated in the above post: Why is it possible to cut open-cell foam, but per your statement, you can’t cut the excess insulation if it’s closed-cell foam?

    I also wondered if you had considered putting foamboard insulation around the basement walls and foaming over that. I’ve read the foamboard also acts as a vapor barrier above 1 1/2″ thicknesses, and should be able to be covered with spray foam insulation. Basically I’m looking to save some cash while getting 3-4″ of insulation on my basement walls.

  3. Fred says:

    Jeff, good questions. Closed cell foam dries rock hard. Open cell foam stays spongy. It’s easy to sheer of open cell phone. Closed cell foam is like cutting wood (almost). Just not practical.
    We considered just about everything for the basement before settling on closed cell foam. What you describe sounds like a lot of work. First, closed cell foam serves as a vapor barrier (you do not need polystyrene board or anything like it). Open cell foam does not. I would not install open cell foam on walls. If you ever get a moisture problem from the outside, open cell foam is a haven for mold. Just don’t do it. Put 2 inches of closed cell all around your basement – that’s all you’ll need and it’ll be plenty warm and proper. (2 inches of closed cell is about R13, but R values are misleading because unlike fiberglass, closed cell doesn’t leave any gaps for air flow. it will be FAR more effective than R-13 batts).

  4. Ben S. says:

    My wife and I are going to be building a new home this spring and have been told that insulating our basement with closed cell spray foam and our exterior framed walls with open-cell foam was the way to go. Is this true or the best way and if so why? Is it because the basement needs a good vapor barrier and the framed walls need some air movement to allow things to dry so mold and mildew don’t form. Also what would be the way to insulate the attic. We live in central Iowa so we get some pretty cold winters as well as some hot and humid summers. Any advice would be greatly appreciated.

    Thanks, Ben

  5. Greg says:

    Don’t use ANY spray foams. You would be wasting your money. Insulated wall makes up less than 10% of the avg homes envelope. Even your walls are only going to be @50% insulation, the rest is doors windows, studs, and plates. Buy R-15 batts and make sure the home is sealed. Central Iowa should be like R-49 minimum in the ceiling, spray foams don’t even reach R-30 (what a joke huh!), install R-60 loose fill for less than the price of any foam, and enjoy it’s superiority. Too many goons on the web think foam is new and cool, but it has been around for decades and never made it past 5% of the market share FOR A REASON. If somebody is pushing foam, ask them for their energy license information. I am BPI certified, CAN06347, is my #. Spray foams are snake oil! Trust me!

    • Miles says:

      And 8 years later, Greg is still wrong. Citing a misapplication of spray foam has nothing to do with the exceptional performance of spray foams used correctly. BPI certification means very little–basically a pay-to-play seal with little expertise needed. No one gets a home to closed-cell numbers with fiberglass, especially. Ridiculous.

  6. Greg says:

    There are R-15 fiberglass batts for 3.5 inch stud bays, and dense packing it in for a BIBS style installation can bring you R-4.5/inch. Better than open cell, less price. Don’t talk about fiberglass R-values not comparing to foams, have you done your own professional testing? Some foam goons like to find a leaky house with batts and blame the batting, instead of the leaks. I tested a house last week tighter than any foam house I have tested, and they used a few cans of great stuff, mainly sealed all osb seams with tape/caulk/mastic, and I tested it before it was drywalled. If you have dense packed fiberglass, and a QUALITY air barrier on both sides, IT WILL PERFORM TO THE R-VALUES IT IS RATED AT, WHICH IS SUPERIOR TO OPEN CELL FOAM, AT A LOWER COST. Let me save you the time of explaining all of the reasons foam is not a smart choice, and explain the MAIN reason. You will spend 10$/month more on your mortgage paying for the extra price of foam, and if you compare a home with foam on the roof deck vs. a very properly done fiberglass/cellulose loose-fill home where it is installed on the ceiling, the foam will actually add to your energy bill as well. Double whammy, but regardless, the added costs of foam annually on your mortgage will most often times out weigh the savings. We build over 25 homes a year, and have for decades, we have gone over the numbers many times with REMrate, our HVAC professionals, and our Realtors for resale value information. SPRAY FOAM DOES NOT MAKE SENSE!!!!!!!! Unless you can get it done for about half or one quarter of the avg going rate.

  7. Peter Williams says:

    We live in an 1890’s frame house in central Texas, built on brick piers with all cedar beams, joists, etc. Have good crawl space. We need to insulate floors on the first floor; they get very cold in the winter. Joists are +/- 10″, but are NOT on standard 16″ spacing… spacing varies from 20-24 inches, so batt insulation under the floors will be VERY DIFFICULT. Can we foam under the floors? Should we consider closed cell or open cell foam? How thick? Are there applicators in the Bryan/College Station area?

  8. WE constructed a modified Swiss Chalet 35 years ago at zip 18801 in PA. Because of moisture and frost concerns and it being built on the side of a mountain, we constructed it on 12″ to 18″ telephone poles. We want to better insulate the floor (which is exposed under the house) with closed cell foam. The installer claims that 2″ would be sufficient but I am concerned. I thought that that area should have R-38 for this application. The project is just over 1000 square feet and the installer wants an additional $1,000.00 for each inch over the 2″ he recommends.

    What say you?

  9. Gil says:

    I live in North Dakota and I want to insulate my garage. My question is for the ceiling. I don’t know which route to go, spray foam, or fiberglass batts? It get’s pretty cold here in the winter and I’m trying to get the job done right and try and save a few bucks in the process. Any advice?

  10. Bruce says:

    Metal building in a hot sunny climate – central Texas. What would you use for the ceiling? Getting batts or board to stick would take a lot of effort to get it to stay in place, some kind of support structure between widely placed joists. ON a hot tin roof (Galvalum) will foam – open or closed – break down or stick and stay?

  11. craig says:

    13 yrs later and your still wrong
    about spray foam i filled rim joists in basement using open cell spray foam i filled entire cavity using cans of expanding foam from menards at 4 bucks a can , i worked at my own pace . what a differance it has made in basement walls are not insulated and thats ok i used 100 cans per wall

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