Two photo frames showing closed-cell spray foam insulation and open-cell spray foam insulation up close with the caption "Open-Cell vs. Closed-Cell Spray Foam Insulation"

Choosing the type of insulation to use when you are putting insulation in your home is an important decision. If you’re thinking of installing spray foam, there are two main types: open-cell or closed-cell. We’re going to break down the differences to help you decide which will work better in your situation.

Open-cell spray foam insulation is cheaper, expands more, and allows more air circulation than closed-cell spray foam. Closed-cell is more expensive, doesn’t expand as much, and seals well enough to act as a vapor barrier. It also has about twice the R-value of open-cell spray foam insulation.

There is a lot to understand about what makes these two foam insulation types different. Here you will find more helpful information about spray foam insulation in general, what the differences are between open-cell and closed-cell spray foam insulation, how it’s applied, and how to know which one is right for you.

What Is Spray Foam Insulation?

Let’s start things by giving a little bit more information on what spray foam insulation is in general. It’s an insulation that is chemical-based and mixed on the worksite by insulation contractors, then applied to the desired location with a sprayer. Spray foam is typically used to insulate walls, floors, and ceiling cavities. Because of its structure, foam insulation doesn’t compress, sag, or settle over time, making it a strong choice for insulating your home. Both open-cell and closed-cell spray foam can last for an extremely long time.

Differences Between Open-Cell & Closed-Cell Spray Foam Insulation

The difference between open-cell and closed-cell insulation is in the small cells, which are similar to bubbles. As the names suggest, the bubbles in open-cell spray foam insulation are open, allowing both air and water to pass through and lending an overall softer structure. The bubbles in closed-cell spray foam are closed, blocking the movement of air and water and making it more rigid. Both can provide an air seal, but only with an applied thickness of 2 inches for closed-cell, and 3 inches for open-cell.

Possible Problems With Spray Foam Insulation

One thing that isn’t as good about spray foam is it’s much more expensive compared to something like fiberglass or cellulose insulation. Closed-cell is the more expensive of the two spray foam insulation types, mainly because it doesn’t expand as much so it requires a lot more to get the job done.

Spray foam can also be a big fire hazard because of spontaneous combustion that can occur because of an exothermic reaction if the foam is not applied correctly. If a house catches on fire from another cause, spray foam is extremely flammable and also creates toxic smoke.

If it’s not mixed and applied properly, off-gassing (which basically means when something gives off a typically harmful chemical in the form of a gas) could cause harmful health issues, or aggravate existing conditions like asthma. Interested in a healthier option? Click here.

It’s important to understand these downsides to spray foam. While it’s extremely popular because of its effectiveness, it won’t be appropriate for every situation.

Open-Cell Insulation

Structure

Open-Cell insulation, as mentioned above, expands more rapidly. This creates a much more open, bubble-like structure. This openness in the structure makes this type of insulation more flexible. In addition to being more pliable, open-cell insulation is much lighter. Because of its pliability, it’s also easier to remove. Plus, it can insulate places that are harder to reach like corners, holes, and other types of nooks.

Moisture

Another quality of open-cell insulation is that it allows the movement of water through it. But because it’s not an organic material, it does not encourage mold growth. Once the insulation is dry, the effectiveness remains uncompromised. It simply allows a pathway where water and water vapor can move in and out of a specific area.

Good brands of open-cell spray foam can retain anywhere from 5% to 70% of their weight in water. If you live somewhere that has consistently high humidity, open-cell insulation may prove to be less beneficial because it will allow outdoor moisture into your house. You can have a vapor-retardant sprayed over the insulation, which will help to minimize this problem.

Multi-colored photo representation of a sound wave. Open-cell spray foam insulation in particular is good at reducing noise inside your house.
If you’d rather see sound waves than hear them, open-cell spray foam is your best bet.

Sound

One great thing about open-cell spray foam insulation is that it absorbs sound well. This comes back to its structure, once again. Remember your elementary school science classes? Sound waves travel through the air until they bounce off of something. When they enter all the little spaces inside open-cell spray foam, they bounce back and forth until they’re absorbed, never reaching your eardrums.

R-Value

As mentioned earlier in the article, open-cell spray foam insulation has a smaller R-value than closed-cell foam. The R-value ranges from 3.5 to 3.8 per inch for open-cell foam. R-value stands for the capacity the material has to resist heat flow. The higher it is, the greater the insulating power.

Cost

Its cost is also much more affordable than closed-cell. Open-cell expands pretty much as soon as it’s applied and expands a lot more than closed-cell foam does. Because of this, you need less to cover the square footage of the area you want.

Closed-Cell Insulation

Structure

Closed-cell insulation is called this because the air pockets are grouped closely together, creating a denser structure. The expansion rate of closed-cell spray foam is minimal compared to open-cell insulation. This lack of expansion and its rigid structure make it much more durable. It won’t easily be damaged, even while it’s still exposed. It can even make the structure of your home stronger. It has a medium density of about 1.75 to 2.25 lbs. per cubic foot.

Moisture

The closed structure makes it much more difficult for water vapor to travel back and forth. This can actually be a bad thing, because it could conceal a leak until the water builds up, causing a much bigger problem later on.

R-Value

It has a much higher R-value, usually around 6.0 per inch, absorbing about twice as much heat as open-cell spray foam. This makes it very effective in areas with extreme temperatures and high humidity.

Cost

The lack of expansion means that it takes much more material to insulate an entire area completely. Obviously, this means that it is much more expensive to use. Installation costs are going to be higher, as well.

Photo of hands on a calculator and a laptop keyboard with a pink ceramic piggy bank, ink pen, papers, and stacks of coins in the background.
Your budget will definitely influence your decision on which kind of spray foam insulation to use.

Which Type Is Better For You?

In general, spray foam insulation is a great solution for filling in all kinds of cracks and spaces. It can also be added to existing walls without tearing them open. Now you know about the different types of spray foam insulation in-depth. Here’s a quick review of how these two different types of insulation work.

Because open-cell spray foam has a much lower R-value, it’s not as suitable for places with extreme temperatures. Heat and humidity can get through it more easily. Open-cell is better for smaller, inaccessible areas because of its soft structure and ability to expand. It also dampens sound really well.

Closed-cell spray foam has a higher R-value, so it works well in places that have more extreme temperatures. It does not allow water to pass through it, but this means it could conceal leaks.

In the end, whether you go with open-cell or closed-cell spray foam will depend on where you live, your budget, and your goals for the space you are insulating. Happy renovating!

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2 Comments

  1. Hi Erin,

    If I go with foam spray in my attic and a company sprays it on my roof plywood, what happens when I need to have my roof replaced and the roofers pull off the plywood. Does the foam come off with it?

    Would you mind emailing me your answer? Thanks, Elise

    1. Hi Elise,

      Thanks so much for your question. I can’t say for sure in your particular situation whether the foam comes off with it. I think it depends on many factors for your particular house. My best suggestion is to call three or more spray foam companies to ask them and hopefully they will give a consistent answer on that, perhaps after coming out to take a look at the attic and roof. Good luck! – Erin

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