I often talk about the benefits of foam in soundproofing projects, but this typically relates to acoustic foam. But I was recently asked: does closed cell foam absorb sound? Here’s a quick answer:
Closed cell foam does absorb sound and is more effective against low frequency wavelengths. It’s a denser material than acoustic foam, and so is used for sound dampening and insulation rather than absorbing echo. It’s best to include both open and closed cell foam.In this article, I’ll cover what exactly we mean by closed cell foam, how it differs from open cell foam, and when to use it.
Also, read – Does Spray Foam Insulation Reduce Noise?
What is Closed Cell Foam and Does it Absorb Sound?
Simply put, closed cell foam is a dense material made from foam. But this is quite a general definition and covers a wide range of different products.
A more technical definition of closed cell foam is a product in which the cells are completely closed in, rather than being open and connected to other cells.
It’s made by subjecting a rubber base to gas under high pressure. This creates tiny air bubbles and decreases the material’s density.
Products you might be familiar with include:
- EVA foam
While these are all closed cell foams, not all are suitable for soundproofing projects. Of course, density is important, but you don’t want something too dense, such as PVC.
The difference between closed cell and open cell foam is pretty obvious: open cell foam has a more aerated structure, and its cells are connected.
Acoustic foam is a popular type of open cell foam, and is used to absorb echo and reverberation.
But while closed cell foam does absorb sound, its application is slightly different.
This is because, along with absorbing sound, it works quite effectively as a sound dampener too.
Sound absorption is the process of a material converting sound waves into heat energy as they pass through it.
This happens when a sound wave, which is vibrational energy, expends some of this energy to make the particles vibrate. In the process, it’s converted into heat energy.
Dampening, on the other hand, is the process of reducing vibrational energy before it becomes a sound wave. Closed cell foam is effective for this because its density prevents sound waves from passing through.
A good example to explain this is the rubber feet on a washing machine. Without these, the machine would rattle and create lots of noise because it vibrates when in use. With the rubber feet, however, much of this vibrational energy is absorbed.
So, closed cell foam does absorb sound but is useful in different situations to open cell foam. For best results in a soundproofing project, you’d want to use both.
Differences Between Open and Closed Cell Foam
I’ve already touched on the major difference between open and closed cell foam. This structural difference means each product has its own specific uses in a soundproofing project.
Closed cell foam, for example, would be used as insulation. You might use it:
- As floor underlayment
- As vehicle insulation
- As part of a DIY acoustic panel
- To muffle rattling appliances
One of its most useful properties is that it doesn’t compress in the same way as open cell foam. This is because it’s already quite dense, and so doesn’t have as much room for compression.
Importantly, this makes it effective against low frequency sound waves. They expend less energy and can travel further, but the foam’s density means there’s simply more of it to vibrate.
Open cell foam does still have its uses in a soundproofing project. It’s most commonly used for acoustic management rather than blocking or dampening sound waves.
For example, the foam panels you’d find on a wall in a recording studio are open cell foam.
Their structure makes it much easier to trap stray sound waves and prevent them from reflecting off the flat wall behind.
This means that, unlike closed cell foam, you can’t have any obstructions between open cell foam and the noise source.
Foam panels need to be the last thing you install, as they’re designed to trap sound waves rather than prevent them passing through a surface.
Open cell foam is less effective at absorbing low frequency waves. However, you can buy bass traps to overcome this issue.
These are still made from open cell foam, but are built differently. Their only real downside is that they’re most often made for corners, meaning you’re limited in where you can put them.
- Closed cell foam does absorb sound
- But it also dampens sound waves due to its density
- You use it more for insulation than acoustic management
- But using both open and closed cell foam is best
How and When to Use Closed Cell Foam
There are various applications for closed cell foam in a soundproofing project, some of which I’ve mentioned above.
One of the best ways to use it is as a component in DIY soundproof drywall.
This is a surprisingly easy thing to make, as you just need to do some sticking. Obviously, you’ll need some DIY knowledge to hang the drywall after, but that’s not too hard either.
For this you’ll need:
- Drywall sheets
- Closed cell foam
- Mass loaded vinyl (Amazon link)
- Green Glue (Amazon link)
When it comes to choosing closed cell foam, your options are almost endless. A budget-friendly option would be something like neoprene sheet roll (Amazon link) or even some yoga mats.
Drywall usually comes in 4ft x 8ft panels, so this will be your standard working size. Of course, it’s worth cutting the panels to size before you start working if needed.
The method is as follows:
- Use a drywall layer as your base and coat the backside in Green Glue.
- Lay a sheet of MLV down and let the adhesive dry.
- Build up a core of closed cell foam, which should ideally be about 1” thick.
- Add another layer of MLV on top.
- Add more Green Glue and then finish with a final layer of drywall.
- Once everything is dry, you can hang it as normal.
Bear in mind that Green Glue isn’t an adhesive, it’s a sound dampening compound. Therefore you’ll need to use actual glue, such as vinyl cement or PVC glue.
On its own, drywall isn’t a good sound blocker. But adding a few layers of drywall with a core of closed cell foam makes it much more effective at blocking and absorbing sound waves.
Importantly, too, combining several products like this makes it good against a range of frequencies, and against both impact and airborne noises.
Obviously, this soundproof drywall will be nearly 2” thick, so bear this in mind when it comes to actually installing it.
Some Final Thoughts
Hopefully, this article has clarified whether closed cell foam absorbs sound. The answer is yes, but it has a range of other useful properties too.
As I’ve mentioned, you’ll want to use both open and closed cell foam in your project because they do different things.
The best advice I can give is to assess your project and budget to see what would be the most effective product for your needs.