Open Cell vs Closed Cell Foam

Open Cell Versus Closed Cell Foam:
What's the Difference?

Open Cell Versus Closed Cell Foam:
What's the Difference?

Open cell foam or closed cell foam, which type do you need? If you’ve found your way here, you’re probably in the middle of deciding between the two. Our focus at Second Skin Audio is on automotive insulation and soundproofing, but the same base knowledge applies to other industries too. Both open cell foam and closed cell foam are effective insulators, especially in vehicles, but they have different strengths and weaknesses.

Read on to learn everything you need to know about open cell foam vs closed cell foam and how to use each as an effective soundproofing foam in your vehicle.

Open cell foam or closed cell foam, which type do you need? If you’ve found your way here, you’re probably in the middle of deciding between the two. Our focus at Second Skin Audio is on automotive insulation and soundproofing, but the same base knowledge applies to other industries too. Both open cell foam and closed cell foam are effective insulators, especially in vehicles, but they have different strengths and weaknesses.

Read on to learn everything you need to know about open cell foam vs closed cell foam and how to use each as an effective soundproofing foam in your vehicle.

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 as the memory foam mattress topper on your bed or the sponge you use to wash your car. It’s springy, pliable, and absorptive. Think of closed cell foam as the chunk of styrofoam that protects your new TV in its box or the foam back roller you got from the chiropractor. It’s more rigid and durable.

As you might be able to guess, both open cell and closed cell foam are effective in automotive sound and heat insulation, but they're relative strengths sometimes mean they should be installed in different areas of the vehicle. Closed cell foam is a great insulator and sound isolator. We often use it as a decoupler behind rattling plastic panels. Open cell foam is perfect for areas where it’ll be able to stay fluffed out and absorb sound waves (like inside door panels or in the back of a cargo van). While you can compress open cell foam, you wouldn’t want to because the less air space inside it, the less effective it is as a sound absorber.

Hydrophobic Open Cell Foam

I feel like we should stop here to make something very clear about open cell foam. Unless it is treated to be hydrophobic, it will absorb too much water. Cars are not perfectly watertight, so open cell foam that will absorb water is at risk of become a hotspot for mold in your car. Black mold can literally kill you. Sorry to be dramatic, but we’d only put open cell foam in our cars if it has some level of water resistance. We give our hydrophobic melamine foam a proprietary water resistant treatment to solve for this issue.

 

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

Measurable Open Cell Foam Closed Cell Foam

Density

Lightweight and spongy

Higher density (still lightweight)

Durability

Soft and flexible; easily compresses

Flexible but resists compression; adds structural support

R-Value

Average 3 to 4 per inch

Average 3 to 6.5 per inch

Permeability

Permeable to air and water

Semi impermeable to water; can be an air barrier

Sound Isolation

Superior acoustical absorber

Passable acoustical barrier

Heat Insulation

Used in dry conditions

Useable in moist or humid conditions

When it’s open cell foam versus closed cell foam, each foam has situations where it’s your best option. From a pure sound proofing point-of-view, open cell foam is the winner because it’ll actually absorb sound waves. Closed cell foam is just so much more durable that it can be used in a wider variety of situations. When it comes to automotive sound and heat insulation, they are sometimes interchangeable and sometimes there’s a clear preference.

Second Skin Open Cell and Closed Cell Foams

Second Skin Audio manufactures both types of foam right here in the USA. From the hydrophobic melamine foam Mega Zorbe (the foam comes from Germany, but we treat give it a proprietary hydrophobic treatment here in the USA) to the super strong, rubber infused closed cell foam OverKill Pro, we have every type of foam insulation your vehicle could need.

 

Take a look at our most popular sound-absorbing automotive insulators:

Measurable Mega Zorbe OverKill OverKill Pro

Size / Sheet

8 Sq Ft

9 Sq Ft

9 Sq Ft

Thickness

1/2 inch

1/8 inch

3/8 inch

Weight / Sheet

0.20 lbs

0.54 lbs

1.35 lbs

Compressability

High

Low

Low

Temperature Range

-300 F to 350 F

-40 F to 165 F

-40 F to 165 F

R-Value per Inch (R-Value)

4.16 (2.08)

4.33 (0.54)

4.33 (1.62)

Flame Resistance

Pass

Pass

Pass

Water Resistance

Medium/High

High

High

Certification Level

Aerospace Approved

OEM Approved

OEM Approved

How to Use Open Cell and Closed Cell Foam in Your Vehicle

Both open cell and closed cell foam have their relative strengths. If you have rattling plastic panels, start with closed cell foam. Depending on the amount of space behind a plastic panel, go with either the 1/8” thick OverKill or 3/8” thick OverKill Pro. Both will decouple those hard rattling surfaces, and cut the noise level in your vehicle. Honestly, you can use closed cell foam just about anywhere in your car that you want to add insulation or decouple rattles. Two examples we see often are as extra insulation above your headliner or as a decoupling layer below a mass loaded vinyl noise barrier.

Where to install closed cell foam:

  • Rattling plastic panels
  • Doors
  • Floor
  • A, B, C pillars
  • Above the headliner

 

Open cell foam is less durable, but it’s the clear best option for absorbing unwanted noise. Over the last few years, hydrophobic melamine foam (HMF) has established itself as the best material for improving automotive acoustics. The key is that it needs to be exposed to the sound waves to do its best work. We most often see it used in the door cavity to clean up speaker back waves and in the cargo area of commercial vans. In both places, it’s exposed to sound waves without the risk of too much physical abuse. Another good use for HMF is above your car’s headliner, where it’s an excellent insulator and will absorb some sound. Hydrophobic melamine foam will absorb sound anywhere you install it, just make sure there’s enough space for it to stay fluffed out and keep absorbing those sound waves.

Where to install open cell foam:

 

Again, keep in mind that although closed cell foam is resistant to water, dirt, and intermittent flames, it isn’t meant to be installed next to a heat source. We don’t recommend installing OverKill Pro anywhere it’ll be regularly exposed to heat over 180°F. For high heat applications, you should be looking at a car heat shield, like Mega Block, where we’ve added a reinforced heat shield to our hydrophobic melamine foam. Its temperature rated up to 1000°F.

Final Thoughts

Both open cell and closed cell foam are useful for vehicle soundproofing and insulation. Open cell foam absorbs sound, but closed cell foam is more durable. Both are great for insulation. Hopefully you now have a much better understanding of which one will be right for your vehicle.