Today, we’re examining another material some people use to get out of having to pay for professional acoustic equipment. But can styrofoam be used for soundproofing?
I’m going to make an educated guess and assume that styrofoam probably won’t be a great noise blocker. Whether it’s a good sound absorber remains to be seen, but I’m not too optimistic on that score either. So if you were looking for a quick answer, that would be it.
If, on the other hand, you enjoy learning about materials and their soundproofing uses, stick around. We’re going to delve deeper into the acoustic properties of styrofoam right after I explain what makes a good soundproofing material in the first place. But first, let’s take a moment to look at styrofoam itself.
What Is Styrofoam?
I must admit, I’ve never been particularly curious about what styrofoam was. It was simply the white stuff that made up the cushioning inside of my packages. Sometimes, it comes in the shape of whatever product I bought, providing firm support, but I usually see it flooding the box in the form of loose peanuts. But what is it?
Closed-Cell Extruded Polystyrene (XPS) Foam
Well, Styrofoam is actually a brand name for the closed-cell extruded polystyrene (XPS) foam. The material was originally invented by Swedish inventor Carl Munters. But in the late 1940s, Dow’s Chemical Physics Lab bought the patent to keep developing the formula. The result was a lightweight and somewhat water-resistant, bluish insulation material.
Generally, XPS foam is used as sheathing and pipe insulation, under roads, and to provide structure for floral arrangements. But as you might have suspected, that’s not exactly the styrofoam we know and use.
Expanded Polystyrene (EPS) Foam
In North America, the word “styrofoam” refers to a similar yet slightly different material — expanded polystyrene (EPS) foam. To get slabs of the stuff, manufacturers first expand individual polystyrene beads then fuse them in metal molds. That allows them to shape the material however they want, which is why EPS foam is so versatile. We use it for disposable coffee cups, food containers, and packing peanuts, among many other things.
But technically, this material isn’t “styrofoam.” Still, since that’s the term most people use, don’t be confused if I keep using it throughout this article, too. Just assume I’m talking about EPS foam.
What Makes a Material Good for Soundproofing?
Now, we’re all clear on the origin of XPS and EPS foam and why we tend to mix them up. However, we’ve gotten no closer to determining whether either of those materials is good for soundproofing. Still, before we can talk about the acoustic properties of EPS foam, we have to lay the groundwork. So let’s talk about what makes a material good at soundproofing.
When it comes to soundproofing, any materials you use have to excel at either blocking or absorbing sound. To achieve either of those results, they have to have one or more of the following acoustic properties.
Mass and Density
Mass and density are incredibly important if you need to block sound from passing through a certain surface. That’s why most of my soundproofing guides rely on thickening up whatever surface you’re trying to reinforce with various materials.
But if you’re looking for a way to understand this principle, look no further than mass loaded vinyl. MLV is a material that exemplifies both of those features. It’s usually thick and heavy as a result of having an incredibly dense structure. But despite that, the material is also very flexible, which makes it relatively easy to work with.
Softness and Porosity
Even if the material you’re working with doesn’t have great mass or density, it could still have desirable acoustic properties. The next properties you’ll want to look out for are softness and porosity. Many items check both of those boxes, including carpets, curtains, and blankets. These are all sound absorbers, which means that they trap any soundwaves that come into contact with them.
But of course, density and mass can help these products perform even better. Without them, you might claim that a thin layer of fleece would effectively muffle noise. After all, that would be both soft and porous.
However, for our imaginary fleece to become a true sound absorber, you’d need it to be thick and heavy too. That would make it more effective at trapping the soundwaves until they run out of energy. I’ve explained this principle in more detail in my article about acoustic fabric panels, which also happen to be a fantastic example of everything I’ve been talking about.
Noise Reduction Coefficient Rating and Sound Transmission Class
The Noise Reduction Coefficient rating system is another thing I’ve explained in the article I’ve linked to above. Basically, it’s a scale we use to “grade” acoustic products based on the percentage of frequencies they can muffle. The ratings are given on a scale of 0 to 1. Having a rating of 0.95 means that a product is capable of muffling 95% of the frequencies that are bouncing around the room.
Sound Transmission Class is another rating system we use to evaluate various materials based on how well they reduce noise. I’ve previously used it to explain the process of buying soundproof doors. That’s the one time when you really need to pay attention to those STC levels. If one door has an STC of 35 while another is a level 55, and their prices are in the same range, you should get the one with the higher rating.
Using Styrofoam for Soundproofing
Now that we know what we’re looking for, can we say that we’ve found it in styrofoam? Let’s find out.
Styrofoam Is Lightweight and Hollow
On paper, styrofoam has a density range between 11 and 32 kilograms per cubic meter, which translates to anywhere between 0.68 to 2 pounds per cubic foot. Conversely, ⅛-inch thick MLV has a weight density of one pound per square foot. If you don’t take into account the structural differences between the two materials, you might think that they’re equally good.
However, styrofoam simply isn’t capable of blocking any noise you point at it. Unfortunately, it doesn’t have the mass or density to manage it. It’s not merely lightweight — it’s actually between 95 and 98% air. On the one hand, that means that it’s pretty cheap, but that means nothing if it’s not effective as well.
Between that air content and the closed-cell structure of the material, styrofoam isn’t a great barrier against air which, as you know, carries sound. It’s difficult to think of a feature that could save it at this point, but let’s keep going.
It’s Rigid and Tough
Unlike any of the acoustic materials I’ve mentioned, styrofoam is generally hard and certainly unbending. On its own, those properties don’t make it unusable. If nothing else, they make it easy to cut through, which can help with the eventual installation process.
However, keep in mind that EPS foam is also fairly fragile — just think how easy it is to break! That means that it won’t be able to properly absorb or deflect soundwaves. I’d even say that bass vibrations might be particularly damaging, maybe enough to completely ruin the material within a few years.
Simply put, I don’t believe styrofoam can bend in the way soundproofing materials must. Of course, before I can officially pronounce this a closed case, there’s one last thing we ought to consider.
Nrc Rating and Sound Transmission Class
As I have previously explained, a Noise Reduction Coefficient rating is typically only given to professional acoustic products. However, I have found some information about the way styrofoam has performed on these tests. According to some sources, styrofoam usually has an NRC rating of about 0.2 — which is nothing to write home about. Remember, that means that it’s only able to muffle 20% of the complete range of frequencies.
There’s no conclusive information about the sound transmission class of styrofoam — but that’s not surprising. However, adding a 2-inch panel of EPS foam between two layers of half-inch-thick drywall while leaving an air pocket inside the wall can increase its STC by 5 or 6 levels (from 35 to 40). That’s comparable to the kind of absorbency you might get from resilient channels.
Some Additional Concerns
In any case, if you’re going to use styrofoam, you might as well hide it inside a wall. Some building regulations even demand that you keep EPS insulation behind drywall, sheet metal, or concrete.
As you can imagine, the material is highly flammable — despite being an otherwise decent thermal insulator. In addition to being flammable, styrene may also be cancerogenic, so there are plenty of reasons not to have it out in the open.
What’s more, there are environmental concerns as well. Remember, styrofoam (or EPS foam) is technically a thermoplastic polymer. Therefore, it’s about as biodegradable as any other piece of plastic — which is to say, not at all.
Even worse, some land and marine animals have shown that they can’t distinguish between styrofoam and food. So if you’ve ever carelessly discarded your packing peanuts, you might have inadvertently fed them to some poor creature.
Is Styrofoam any Good?
Even if styrofoam reminds you of some acoustic products you’ve used before, looks can be deceiving. It may be as lightweight as acoustic foam, but it’s nowhere near as effective.
Going by all the information I’ve just laid out, it simply isn’t the best material you could use to soundproof your home. And even if you decide to use it, you shouldn’t leave it exposed — that is, if you don’t want it to catch fire.
Ultimately, while styrofoam may be able to dampen the jostling your Amazon package has to withstand, it probably can’t dampen the sound of your enthusiastic jam session. So if I were you, I’d start looking into other materials. And if you’d like to learn whether other commonplace substances would be good soundproofing materials, you could read this article about the acoustic properties of wood.