Open Cell Vs Closed Cell Foam: What's The Difference?

What's the Difference Between Open Cell and Closed Cell Foam?

The main difference between open cell and closed cell foam is right there in the name. Open cell foam has open cells that allow air and liquids to permeate the material — whereas closed cell foam cells are relatively impermeable. For this reason, open cell foam is much softer and less dense than closed cell foam. Closed cell foam requires more plastic to manufacture, so it is therefore more durable, water-resistant, and often has a higher R-value.

Think of open cell foam like the memory foam mattress topper on your bed or the sponge you use to wash your car—soft, flexible, and absorbent. In contrast, closed cell foam is more like the rigid styrofoam that protects your new TV in its box or the firm foam roller from your chiropractor—dense, durable, and sturdy.

Both types of foam are effective for automotive sound and heat insulation, but their unique properties make them better suited for different areas of a vehicle. Closed cell foam is an excellent insulator and sound isolator, often used as a decoupler behind rattling plastic panels. Open cell foam, on the other hand, is ideal for areas where it can remain expanded to absorb sound waves, such as inside door panels or in the cargo area of a van. While open cell foam can be compressed, doing so reduces its air space and diminishes its effectiveness as a sound absorber.

Hydrophobic Open Cell Foam

Let's take a moment to clarify something important about open cell foam. Unless it's treated to be hydrophobic, it can absorb too much water. Since cars aren't perfectly watertight, untreated open cell foam can become a breeding ground for mold—and black mold is a serious health hazard. Not to be overly dramatic, but it can be dangerous. That’s why we only use open cell foam in vehicles if it has some level of water resistance. To address this issue, we apply a proprietary water-resistant treatment to our hydrophobic melamine foam.

Let's take a quick look at how these two types of foam stack up against one another:

When comparing open cell foam to closed cell foam, each has its ideal applications. From a purely soundproofing perspective, open cell foam is the better choice because it actively absorbs sound waves. However, closed cell foam is far more durable, making it suitable for a wider range of uses. In automotive sound and heat insulation, the two foams can sometimes be interchangeable, but in certain situations, one is clearly the better option.