Open Cell vs. Closed Cell Foam: Understanding The Differences


Open Cell vs. Closed Cell Foam: Understanding The Differences

Foams are used by many industries to insulate against noise, heat and steam, but also to filter air or keep air out. Depending on the type of application and the desired results, you will have to choose between two types of foam: open cell foam and closed cell foam.

It is therefore important that you understand the main differences between these two types of foam in order to make the right choice that will allow you to maximize the performance of your application.

Here is an overview of the characteristics of each type of foam as well as the applications for which each is preferred.

Closed Cell Foam

What Is Closed Cell Foam?

In closed cell foam, the cells look like tiny air pockets stacked on top of each other. These cells form a compact unit that gives closed cell foam a semi-vapor permeability, more rigidity, and the ability to withstand greater pressure. Compared to open cell foam, closed cell foam is about 4 times denser.

Characteristics of Closed Cell Foam

Some of the important characteristics of closed cell foam are:

  • Durable: With cells bunched up closer to each other, closed cell foam is heavier, firmer, more rigid, and more robust to the elements.
  • Water-resistant: The cell structure of closed cell foam won’t allow water to pass through easily, as it is impervious and semi-impermeable to vapor.
  • Higher R-value: Closed cell foam is 3-4 times denser than open cell foam, which means it has a higher R-value of 3 to 6.5 per inch.
  • Less air-permeable: The closed cell nature and higher density of closed cell foam mean it won’t let air pass easily.

What is Closed Cell Foam Used For?

Closed cell foam is an excellent material for acting as an air barrier, seal, or gasket as the closely-packed cells don’t allow air to escape or flow into a room. In short, it is perfect for preventing the air in an air-conditioned room from mixing with the hot air from outside

Similarly, you can use it for heat insulation. The material has high resistance to heat due to its high R-value, keeping internal temperatures stable. That explains why manufacturers use it as thermal foam in the space, transportation, construction, and HVAC industries.

The closed cell structure also means the foam provides good protection against moisture. If you have a building or enclosure in an area that receives plenty of rainfall, closed cell foam will act as a blockade as it is less likely to absorb water. In short, closed cell foams can prevent moisture build-up and mold growth.

Lastly, you can use the foam for noise isolation as the closed cells will act as an acoustic barrier that prevents noise from seeping in or out of a room.

Open Cell Foam

What is Open Cell Foam?

Unlike closed cell foam, open cell foam is full of open-ended cells with a lower R-value. Consequently, the foam is lighter and more flexible. Its cells are further apart, resembling that of a sponge, which makes it air and water permeable. That means it is porous and absorbent.

Characteristics of Open Cell Foam

Some of the important characteristics of open cell foam are:

  • Open cells: The foam cells are not entirely sealed like in closed cell foam.
  • Permeability: Its loose cell structure lets in air and water, which makes it porous and air permeable.
  • Low density: Since its cells are much further apart, it has a lower density, an R-value of 3-4 per inch.
  • Soft and flexible: It is less dense and rugged than closed cell foam, so it is softer and more flexible.

What Is Open Cell Foam Good For?

Of the two, open cell foam is the best material for making reticulated filter foam. The open cells mean they can let in air and water, perfect for filtration. In addition, reticulated filter foam is a low odor material resistant to mildew.

Despite its cell’s open nature, it is a good material for thermal insulation. Although not as good as closed cell foam, it still boasts an R-value of 3-4, which is good enough for heat resistance and insulation in dry conditions.

Consequently, that makes it a suitable substitute for closed cell foam insulation where there won’t be any interaction with moisture. It is the ideal material to keep costs down in a damp-free use case.

Open cell foam is light and flexible, which makes it suitable for smaller fill-ins in hard-to-reach nooks and crannies. Closed cells will only expand about 1” while open cells will expand by about 3’’ and fill those spaces. All these characteristics mean you can use open cell foam in most standard walls.

Moreover, it comes in handy for soundproofing as the open cells offer superior acoustical absorption. Open cell is the material of choice in acoustic foam as it reduces sound waves and echoes within a space.

Open Cell Foam VS. Closed Cell Foam?

When it comes to choosing the right type of foam for an application, there are 5 factors to consider: Air permeability, water vapor exposure, thermal insulation, sound insulation and cost.

Air permeability: For filtration purposes, choose an open cell foam. If you need to keep air out, choose a closed cell foam.

Water Vapor Exposure: A closed cell foam will keep water and water vapor out. Because it is more permeable, open cell foam is more likely to absorb water and have its structure and performance degraded by mold and bacteria.

Thermal Insulation: Both types of foam are effective against heat. The final choice will therefore be determined by exposure to wet or humid environmental conditions.

Acoustic Insulation: Because it is more permeable, open cell foam will be more effective in applications requiring sound absorption.

Cost: Cost is also a determining factor in foam selection. In situations where both types of foam are suitable, closed cell foam will always be the more economical option.


Closed cell foam and open cell foam each have their own unique properties. Understanding the type of application, the desired results and the conditions to which the final product will be exposed will help you choose between a closed cell foam and an open cell foam.

The ID Group can help you find the right foam for your application. We offer both closed cell and open cell foams for all your sound absorption, thermal insulation and filtration needs. Contact us for more information on our product selection and customization services.

Image Source:
Polymer Technologies