Soundproof Foam And Acoustic Foam – Myths & Unbiased Facts


soundproof and acoustic foamI have come across many people who really believe that foam is great for soundproofing spaces such as home recording studios and bedrooms.

I’ve heard all of them mention the term ‘soundproof foam’ which blocks sound and I tell each and every one of them that there is no such thing.

It’s surprising to see so many websites and forums that profess that the cheapest and most effective material to soundproof anything, is foam.

So, as an owner of a home studio and a site on soundproofing, I feel that I have a responsibility to put the facts out there and educate people so that they don’t waste their money on something totally useless as foam.

Yes, foam is useless for soundproofing but the same is not true for sound absorption or acoustics.

That is why ‘acoustic foam’ is for real even though ‘soundproof foam’ is a myth.

The Soundproof Foam Myth

The misconception about foam being soundproof exists mostly because people lack the understanding of the differences between sound absorption and soundproofing.

It is natural to assume that if products like foam absorbs sound, there will be none that is left to escape the room.

Unfortunately, sound is not like a fluid that gets absorbed and trapped in something like a sponge. The way sound behaves needs to be understood clearly here.

Sound waves are nothing but vibrations and when they strike a surface, they tend to vibrate it.

Sound does not ‘pass’ through a wall or ceiling but merely vibrates it. These vibrations are further transferred to the other side and that is how sound transfer take place through walls, ceilings and other surfaces.

What’s a Good Soundproofing Material

Now that we are clear on how sound transfers through surfaces, it is important to know what the basic requirements are for a product to reduce sound transfer.

As I brought out before, sound waves vibrate a surface when they strike it and the intensity of vibrations of the surface determines how much sound is transferred.

So, naturally, we want the surface to resist the vibrations or not allow sound waves to vibrate it.

For this to happen, the object needs to be dense and heavy. A heavy wall, for example, would be difficult to move.

Now it’s easy to see that foam is not good for soundproofing. Ask yourself, how heavy is the densest of foam that you’ve come across?

Not much really and the answer lies in this. Foam can never be made heavy enough for it to become an effective soundproofing substance to reduce sound transfer.

I would like to bring out some of the myths regarding ‘soundproof’ foam and what you should do instead, for actual soundproofing.

After that, I’ll talk about the acoustic capabilities of foam.

1. Walls and Ceilings

The most common myth is that panels made of foam can be stuck on walls and will reduce the amount of sound from entering or leaving a room.

The foam that you see stuck on the walls of studios are not meant for soundproofing but are meant for sound absorption. The products that do the actual soundproofing in a studio are something else.

What You Should Be Doing Instead

You should first of all try to make your walls heavier. You can add mass to your wall by:-

Extra Drywall

Installing an additional layer or two of drywall will help to reduce sound transfer. A 5/8” thick drywall sheet weighs 2.31 pounds per square foot. That’s some serious mass and is a great substance for reducing sound transfer.

Coming back to foam, there are many varieties available and their densities vary depending on the type and grade. However, the foam would have to be several inches thick to match the mass of drywall.

Pros

  • Low cost.
  • Lots of mass.

Cons

  • Effort and workmanship required to install.
  • Involves modification of structures, so not an option for rented apartments.

Mass Loaded Vinyl (MLV)

Unlike foam, mass loaded vinyl is flexible and is dense as well. It is a great way to reduce sound transfer if you don’t want to get into the hassle of installing drywall or you live in a rented apartment where you are not permitted any structural modifications.

Again, the typical ‘soundproof’ foam is no match for the mass of an MLV.

Pros

  • Easy to install.
  • Higher density and mass.
  • Can be used for rooms where installing additional drywall is not feasible.

Cons

Damping Compound

green glue
Image source: greengluecompany.com

Using a damping compound like Green Glue is a smart way of increasing the effectiveness of soundproofing.

The damping compound will be sandwiched between the existing wall or ceiling, and the drywall or mass loaded vinyl that you are installing.

Pros

  • Does not require additional space as it is a fluid which will be sandwiched between two hard surfaces.
  • Cost effective.

Cons

  • Adds to the overall cost.
  • A bit messy which applying.
  • Long curation time.

To know about the effectiveness of Green Glue, I highly recommend you read my article.

2. Floors

When you’re trying to soundproof a floor, there are two issues that you would be looking at.

  • Impact Noise
  • Airborne Noise

Impact noise is the noise caused as a result of footsteps or furniture being moved on the floor.

Airborne noise is the sound that is normally transmitted through the air and these include traffic noise, dog barking, neighbors yelling and everything else.

What would foam do for floors?

Having a foam layer laid out on the floor would help a little in reducing impact noise. How much the effect would be would largely depend on the thickness and density of the foam.

For airborne noise or sound transmission through the floor, foam is ineffective. The same rule of an increased mass requirement would rule out foam as an effective substance for soundproofing.

In this video, the ineffectiveness of spray foam for soundproofing is clearly demonstrated.

What You Should Be Doing Instead

Drywall on the floor is impractical, so that can be considered ruled out. However, a heavy object would deal with impact as well as airborne noise and will be much more effective than foam.

Concrete floors do well but at the same time, concrete is a good transmitter of sound despite having lots of mass.

Before you start, you will need to assess how much sound is being transmitted through the floors. The first thing you should do is seal the gaps/cracks in your house to make a realistic assessment.

Then, if you find that the floors are a problem, you can use any of the solutions given below.

Use a Soundproof Underlayment

This is the best soundproofing option. An underlayment such as the Serena Mat with just 3/8” thickness would weigh 1.4 pounds per square foot.

Pros

  • Easy to install.
  • Made of recycled items.
  • Highly Effective (much more than foam).
  • Can be glued directly to engineered wood.

Cons

  • Very Expensive.

Mass Loaded Vinyl

Mass loaded vinyl can be used as an underlay as well. It has similar properties and functions to the Serena Mat except that it is made of limp mass material whereas the Serena Mat is recycled rubber.

The pros and cons of mass loaded vinyl as brought out earlier are applicable here too.

Cork Underlayment

If you don’t have the budget for a soundproof underlayment, you can go for a ‘sound deadening’ option which is cost effective.

Cork is a very popular underlayment which is more effective than foam and yet, priced at half a buck or less.

Pros

  • Very cost effective.
  • Easy to install.
  • Can be used for most types of floors.

Cons

  • Not as effective as MLV and Serena Mat/Acoustik Mat but far better than foam.
  • Susceptible to moisture. A plastic protective layer is required.

Read about my top pick for cork underlayment.

3. Doors

Though not very often but I’ve also heard of people using foam to soundproof doors. Before we dwell on this, there are three main types of doors that we will talk about here.

  1. Hollow Core Doors
  2. Solid Wood Doors
  3. Solid Core Doors

Hollow core doors are the low cost and light doors which are common in most homes and offices.

Being lightweight, they transmit sound easily. Adding so-called ‘soundproof’ foam will not add enough weight to reduce sound transfer.

What You Should Be Doing Instead

Doors are weak links and soundproofing them are a difficult task. Here is what you can do.

Communicating Doors

The best option to reduce sound transfer is to have communicating doors.

Communicating doors are a set of two doors installed with a gap in between them. The gap of air between them will create an insulating layer which will be highly beneficial for soundproofing.

A gain from 30 STC to 55 STC can be achieved by installing communicating doors. More about these in my article here.

Replace the Door

The second option is to replace the hollow core door with a solid core door. Solid core doors are known to perform better than solid wood doors and have the advantage of being less costly in comparison.

However, it will still be inferior in soundproofing as compared to the communicating door.

Soundproof Curtains

Installing communicating doors or replacing the door would involve some time, effort and money.

If you want to have the least of the three, ‘soundproof curtains’ as the term goes, are an option. I call them noise reducing curtains because they do deaden the sound, but don’t do wonders. And they are much better than foam.

These curtains are heavy and are effective to quite an extent but not as good as the options mentioned before. Nonetheless, it is better to have them than to have nothing at all.

Read my guide on soundproof curtains.

Whichever option you choose, you have to seal the gaps through which sound is allowed to easily enter or leave a room.

The gaps in the door frames, door jambs and under the door would need to be plugged and this can be a painful exercise.

4. Windows

Like doors, you will find windows difficult to soundproof. Windows are thin and the glass does not help either.

Covering the window with foam panels does not help. Using expanding foam in between the cracks and gaps would help but enough to prevent direct leakage of sound.

What You Should Be Doing Instead

Sealing gaps with expanding foam or foam spray is an option but can be messy. It is better to use acoustic sealant instead.

As far as the window itself, adding mass is not easy. The following are the viable options for soundproofing a window:-

Double Glazing or Secondary Glazing

The best option would be to have a two-layered window with an air gap in between. The air gap in between will act as an effective insulating layer for sound.

The types of glass used for this are acrylic or laminated glass. For installing a double glazed window, you would have to remove your existing window.

soundproof windows

Problem with double glazed windows is that they are costly. An alternative would be secondary glazing wherein your existing window will become the first layer and the second layer of acrylic, laminated glass or acoustically laminated glass is simply added.

Between acrylic and laminated glass, the latter will be more effective for soundproofing.

Install a Window Plug

This is a popular one among home theater and home studio owners.

A window plug is a simple way of adding mass over the window to reduce sound transfer. It is also a good way of soundproofing windows without replacing them.

A window plug is basically a box filled with insulation that exactly matches the dimensions of the window and fits in the gap over the window sill.

Details of its construction can be found here.

The substance used for the construction of a window plug is the key. MDF or OSB being dense and heavy are great options. Needless to say, a foam comes nowhere near a window plug in terms of soundproofing.

Soundproof Curtains

Soundproof curtains are a good option for windows too. They are quick and easy to install and don’t cost much. They are not as effective as double glazing or window plugs but as mentioned earlier, much more effective than foam.

For more ways (other than foam), read my article on how to soundproof windows.

5. Ear Plugs and Ear Defenders

Foam is an integral part of ear plugs and ear defenders. And there is no choice really. These cannot be made of heavy stuff as they will cause a lot of discomfort while wearing.

Ear defenders are made of hard plastic on the outer and foam layers on the inside. They do provide protection against high-frequency sound but not so for lower frequencies.

The ear defenders cup the ears with pressure making an airtight chamber. This gives an impression that the foam is blocking sound well.

But, if you are traveling in an aircraft or a bus, you will hear the low-frequency engine noises clearly. The lack of mass would never make an ear defender soundproof.

Acoustic or Sound Absorbing Foam

Now that you are aware that soundproof foam does not exist, let us move on to acoustic foam.

Acoustic foam works fairly well at sound absorption and can be used to acoustically treat a room to improve the quality of sound. It is widely used for treating recording studios and theaters.

To bring out how effective foam is for sound absorption, I would like to compare it to rigid or high-density fiberglass insulation.

There are three important differences between the two types which we need to consider while placing them in a room for improving acoustics.

Cost

Foam wedges are cheaper as compared to fiberglass insulation panels and the more popular choice for recording studios. This is because a fiberglass insulation board needs a frame to protect it from breaking and the panel is required to be covered with fabric so that the insulation fibers don’t fly off.

Foam does not require a frame or fabric as it is strong enough to withstand light stresses and does not have fibers that will fly off.

Health Concerns

Fiberglass fibers are made up of small pieces of glass extruded in fibers and are a health hazard when inhaled. More about health hazards of fiberglass insulation here.

Precautions need to be taken while working with fiberglass insulation. Even when wrapped in fabric, there are chances of the fibers coming out through the pores of the cloth.

There are no such concerns with regard to foam and that is why foam is preferred for small recording studios.

Working with Fiberglass as Compared to Acoustic Foam

Apart from health hazards, fiberglass insulation also causes irritation when it comes in contact with the skin.

No such problems with foam whatsoever.

Sound Absorption

The fiberglass loses on all counts to foam but is the winner as far as the most important factor is concerned.

To acoustically treat a room (like a home studio), you would like to know how well the product (like foam panels) absorbs sound. The more it absorbs sound, the less of it is reflected back in the room.

An important metric for calculation of sound absorption is Noise Reduction Coefficient (NRC).

An NRC of 0 means that there is no sound absorption taking place and the product is totally useless for acoustics. On the other hand, an NRC of 1 indicates 100% absorption.

However, absorption tests also indicate values over 1 even though it is theoretically impossible for substances to absorb more than 100%. There is a technical explanation given by Ethan Winer here but for understanding purposes, NRC 1 and above means perfect absorption.

A comparison between the NRC values of two-inch fiberglass rigid boards and two-inch acoustic foam wedges is given in the table below.

Material 125 Hz 250 Hz 500 Hz 1000 Hz 2000 Hz 4000 Hz Overall NRC
Fiberglass 2” thick 0.17 0.86 1.14 1.07 1.02 0.98 1
Foam 2” thick 0.2 0.29 0.66 0.8 0.89 1.02 0.65

As seen in the table above, the NRC values at 1000 Hz and above are more or less similar whereas at 500 Hz and below, fiberglass outperforms the foam.

Verdict

Acoustic foam will cost lesser than fiberglass, is virtually free of health hazards and much easier to work with.

Acoustic foam can be used effectively to tame mid and high frequencies. However, they should not be used for treating low frequencies.

So, my take on this is that you should have acoustic panels made of foam for the higher frequencies and bass traps for the lower frequencies.

My advice would be this – Don’t go for bass traps made of foam no matter how many positive reviews you find for such products.

Acoustic Panel Placement Plan

A typical placement plan for bass traps and acoustic foam panels in a room are shown below.

placement bass traps acoustic panels

Good places to place bass traps are the corners where the walls intersect and the places where the walls and ceiling meet. These are the areas where low-frequency bass is the maximum.

Acoustic panels will be placed at the reflection points. These are the points on the walls and ceiling where sound bounces off and reflects on to the listening position. Read this article of mine to know more about reflection points and how to find them.

The bass trap placements in corners are marked by ‘1’ and the wall-ceiling ones are marked as ‘2’. The rectangles marked as ‘3’ are for acoustic panels.

The types and dimensions of the traps and panels as given in the figure would be as follows:-

  • Rectangles marked ‘1’ and ‘2’ – Fiberglass bass traps 48” x 24” x 4” (thickness)
  • Rectangles marked ‘3’ – Acoustic Foam wedges 36” x 24” x 2” (thickness)

So, as per the figure, we would need a total of 8 bass traps and 6 acoustic panels.

Recommended Products

The products that I recommend will do a good job for a reasonable price. There are products like the super chunk bass traps which would perform marginally better but are not worth the cost.

Bass Traps

ATS Acoustic Panel 24x48x4 Inches (check prices of these products on Amazon).

bass traps

These products can be straddled across each corner.

The air gap behind the panel will assist in low-frequency absorption. Read my article on bass traps and acoustic panels for a detailed explanation.

Acoustic Panels

12″x12″ Two-inch Thick Foam Wedges by Izo -12 pack (check prices of these products on Amazon).

acoustic foam

These are two-inch thick foam panels that come in packs of 12. Total dimensions of these wedges when placed together (see image) would be 48” x 36”.

To economize, we will be placing only six of the wedges (total 36” x 24” area covered) at each reflection point.

So, you will need only three 12 packs of these products to cover the six reflection points.

Cost Analysis

For the products recommended, let us see how much the cost works out to be. Prices would vary as they are subject to change.

8 x Fiberglass Bass Traps = $71 x 8 = $568

As you will need only three 12-pack foam wedges for the six reflection points, cost of these will be..

3 x 12-pack foam wedges = $35 x 3 = $105

Total Cost of recommended products = $673

This is still too high. To bring the costs down I would recommend going for four bass traps instead of six for the corners of the room.

The corners of the room accumulate more bass than the wall to ceiling intersections, so it’s ok to skip them for now.

This would reduce the total cost of products to $389 which is reasonable.

The cheapest alternative would be to go the DIY route.

Final Thoughts

In this article, I have tried my best bring out the myths surrounding ‘soundproof’ foam by giving detailed explanations and reasoning.

These myths have been around for decades and it is surprising to see them prevalent in these modern times.

The biggest problem is that these myths lead to wrong decisions which prove to be costly.

Foam may be cheap but when you buy in bulk to cover your walls and ceilings and in the end, you get no benefit, imagine what a waste of money that would be.

Foam can be used for improving the acoustics of a room, but with limitations as mentioned earlier in this article. Make sure that you don’t buy foam bass traps as they will not be effective for low-frequency sound absorption.

And last but not the least, if you find the information in this article useful, do share it with your family and friends so that they don’t fall into the soundproof foam gimmick.

Thanks for reading! Before you go, take a minute out and check out the best insulation materials for soundproofing and acoustics which I highly recommend. 

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