What's The Difference Between Closed Cell And Open Cell Spray Foam?

Researching insulation can feel like information overload. R-value. Price. Different materials. Even picking one type of insulation can lead to more details than you ever thought was possible.

This is undoubtedly true of spray foam. There's spray polyurethane foam and injection foam. There are different depths and densities. And trickiest of all, there is open cell and closed cell foam. What does that even mean? If the names are so similar, could the difference be that significant?

At South Central Services, we have installed closed cell and open cell spray foam insulation in hundreds of structures. It's our job to advise customers on which foam–if any–is a good match for their needs.

By the end of this article, you'll know:

• What open cell and closed cell spray foam have in common
• What makes open cell and closed cell spray foam different
• An easy way to remember which foam is which
• Which spray foam would work best for your specific project

Open Cell And Closed Cell Spray Foam: What's The Same?

Open and closed cell spray foam are both types of two-component polyurethane foam. Two liquid chemicals are heated and combined to make spray polyurethane foam (SPF). These chemicals undergo a reaction that creates the plastic foam.

Since both open and closed cell foams are SPF, they are applied with a spray gun. The average observer may not recognize the differences by watching them be applied. However, for a trained professional, open cell and closed cell require different spray techniques to adhere well.

What Makes Open Cell And Closed Cell Spray Foam Different?

Open cell and closed cell foam are different at a cellular level. As you can see from the picture below, the cell structure of each foam is different.

Open cell foam has an open cell structure, and closed cell foam has a compact one. To compare the cell structure, let’s think about sponges and foam boards.

If you’ve ever used a yellow sponge to wash a car, you can understand the cell structure of open cell foam. There are many spacious air pockets in those sponges, and you can compress them tightly.

Foam board has compact air pockets that don’t allow for more compression. If you push on a foam board with your hand, you may only make a small indentation or shallow impression of your hand. Closed cell foam has a similar cell structure to foam board.

The difference in cell structure changes physical properties, including density, R-value, vapor permeance, and air permeance.

Let's look at both kinds of foam in more detail.

Closed Cell Spray Foam

Closed cell spray foam is applied at a density between 1.5 pounds and 4 pounds. 2 pounds, however, is the most common application. It has an R-value of approximately R-7 per inch, depending on the manufacturer. At an inch and a half thickness, closed cell foam has an air barrier and a vapor barrier, meaning it keeps out air and moisture.

The rigidity of closed cell foam can offer structural support and indicates a higher R-value. But the easiest way to remember the features of closed cell foam is to think about the word "closed."

Closed cell foam is "closed" to water and moisture. It will not absorb water or vapors. It is also "closed" to airflow, as it creates an airtight seal.

Where Can Closed Cell Spray Foam Be Installed?

Closed cell spray foam works well in places that can incur moisture because it has a built-in vapor barrier. Closed cell foam resists moisture absorption. Ideal areas to install closed cell foam include:

• Crawl spaces
• Basements
• Foundation slabs
• Ductwork
• Exterior walls
• Roofs

Contractors can install closed cell foam almost anywhere that open cell foam can be installed.

Open Cell Spray Foam

Open cell spray foam is applied at a density of 0.5 pounds, which is why it is also called half-pound foam. Because it is less dense than closed cell foam, it expands more rapidly and has a fluffier, cloud-like appearance.

Open cell spray foam has an R-value of about R-3.7 per inch. Again, this will vary slightly depending on the manufacturer of the foam. While open cell foam has a built-in air barrier at 3.75 inches thickness, it cannot create a vapor barrier due to its open cell structure.

Open cell foam refers to the cellular level. Still, it's easy to remember the features of open cell foam with the word "open."

Open cell foam is "open" to moisture and water. Without added coatings, it is vapor permeable. Open cell can absorb water or vapors unless a vapor barrier coating is added after application.

Where Can Open Cell Spray Foam Be Installed?

Open cell spray foam is best applied in "open" cavities that require a lot of insulation. It is also a functional sound barrier, as it will absorb sound waves.

Open cell spray foam insulation can be installed anywhere fiberglass batts are usually installed. Some examples of ideal places to install open cell foam insulation would include:

• Interior walls
• Exterior walls (with wood substrate)
• Vented attics
• Unvented attics
• In between floors

I Know Which Foam Is Which. Now What?

If you're convinced that spray foam insulation is the solution you need, you need to speak with spray foam contractors. A professional contractor will have the expertise and precision to ensure you receive all the benefits spray foam offers, whether you need open or closed cell foam.

Now that you know the difference between open cell and closed cell, you can:

• Learn how much open cell and closed cell spray foam cost
• Choose which type of spray foam is best for your project
• Discover whether or not spray foam is DIY-friendly