Closed Cell vs. Open Cell Foam

Manufacturing parts and components such as tapes and gaskets often means working with foam. The right foam material can bring the properties you need for your application whether that means creating a seal between parts, absorbing mechanical forces, providing insulation or a variety of other uses.

 

Some of your questions during the material selection process may revolve around cell structure. Namely, should you use closed cell foam or open cell foam? What’s the difference between open cell and closed cell foam? Which type of foam material will have the properties you need?

 

By clearing up the technical difference between closed cell foam and open cell foam, you can pick your foam material with confidence, moving on to other steps of your project.

 

DEFINING CLOSED CELL FOAM AND OPEN CELL FOAM

As their names imply, closed cell foam and open cell foam are defined by cell structure. The tiny cells  that make up each foam material determine its properties. While a closed cell material forms an air barrier that doesn’t allow air or water vapor to move through it, an open cell material is usually permeable by both.

 

• A closed cell material might be a denser, less porous rigid foam, sponge or rubber — it could also be a more flexible foam such as PVC, polyethylene, cork, silicone or neoprene.
• Open cell materials include urethane foam options, such as ether or ester. Natural rubber and both natural and synthetic felt are also open cell substances.

 

While materials of both sides may be interchangeably called sponge, foam or rubber, the technical definitions of those terms are as follows:

 

• Foam is the family of polymers including polyethylene, polyurethane and silicone and PVC.

• Sponge consists of elastomers, like Neoprene and EPDM.

• Rubber is a class of solid elastomers that don’t fit in with the foam and sponge categories.

 

Foam is made with a foaming or blowing agent. When you zoom in visually on closed cell foam or open cell foam materials, you can see the difference — while closed cell structure substances are a network of closed air bubbles, there is empty space in the net-like structure of an open cell material. Some foams polyurethanes, like reticulated filter foam, are so clearly differentiated that you can see their open cell nature with the naked eye, no microscope needed.

 

CLOSED CELL FOAM: WHAT TO KNOW

Closed cell foam and related materials aren’t all the same. Within the overall closed cell category, there are a wide variety of foams and sponges that can fulfill a range of insulation, sealing, attaching and protecting functions. 

 

Traits of closed cell foam materials

Closed cell foam materials may be low or high foam density, depending on what the project demands. Closed cell foam’s permeability and breathability does not change with added density. Since closed cell foam can be made watertight or airtight, it’s the material type of choice for sealing materials and insulation in situations when a vapor barrier is needed to keep air, water, and vapor out of an object.

 

Just as closed cell materials come in many different densities and flexibility levels, from rigid foam to pliable foam, they also cover a broad price range. A low-cost, common polyethylene is a closed cell material, as is a more advanced sponge material like silicone that is impermeable by air or water and offers higher temperature resistance.

 

Common closed cell products

Closed cell foam material options include:

 

• Polyethylene
• Cork and cork rubber
• Neoprene sponge
• PVC foam 
• Butyl rubber
• EPDM
• Silicone

 

These materials cover a wide selection of traits and descriptions, from sustainable materials like cork to oil resistant sponges like neoprene that can be manufactured to fit a variety of requirements. Between these options, it’s possible to create everything from shock-absorbing packaging to tight-sealing gaskets, closed cell foam weatherstripping and much more.

 

OPEN CELL FOAM: WHAT TO KNOW

Open cell foam is different from closed cell options due to the empty space in its net-like structure. While these substances don’t withstand as many elements as closed cell materials, there is still significant variation in chemical composition, use cases and price range.

 

Traits of open cell foam materials

Products made out of open cell foam are typically lower in overall foam density than items made with closed cell materials. They also tend to be softer and more pliable. All of these traits are related to the open nature of the tiny foam cells themselves — these are breathable materials that allow air and moisture to pass through with the exception of a few specialty foams like high-density urethane and expanding foam sealant tape, also known as impregnated urethane or Sure-Seal.

 

With that said, there is variation within the open cell foam family of polymers. From affordable, mass-produced polyurethane ether to a more advanced silicone foam, open cell materials can fill a variety of home insulation, filtering, and cushioning functions.

 

Common open cell products

Open cell foam material options include:

 

• Polyurethane foam (ether or ester)
• Reticulated filter foam
• Microcellular urethane
• Expanding sealant foam

 

While the general rule is to select an open cell material when in need of a  breathable (and often lower cost) option, there are some exceptions. For example, when compressed microcellular urethane options or impregnated urethanes behave similarly to closed cell foam despite their open cell nature.

 

CLOSED CELL VS. OPEN CELL FOAM FOR YOUR PROJECT

The final question of whether your project is better suited to closed cell foam or open cell foam comes down to what you want the material to accomplish. When creating tight seals and gaskets meant to act as a vapor barrier and keep all air and moisture out, a closed cell material is usually recommended . For a softer, lighter option that will let air flow through, open cell materials are an ideal choice.

 

Whether you need insulation, sealants, adhesive foams, gaskets, secure packaging materials or any other kind of solution, choosing the correct cell composition will help you get a high level of performance from your materials.

 

SECURING THE IDEAL FOAM MATERIAL

When you work with an industry-leading foam material provider, you never have to go it alone on any step of your design and manufacturing processes. Selecting the right material is easy when you have advice from professionals, who can tell you whether a closed cell foam or open cell foam is best for your new project.