Does Soundproofing Foam Work Both Ways? (And Do They Keep Sound In or Out?)

“Does soundproof foam work both ways?” The not so uncommon question is naturally a part of every discussion around soundproofing. The answer is a lot more intricate than a simple yes or a no.

Soundproof foam can work both ways if you take care of two things: the material and the geometry. Material has to be uniform on both sides of the foam and geometry has to be curvy/wavy on one side and flat on the other (for mounting on a wall).

However, if you’re aiming to have soundproofing foam work both ways, you need to understand how they work and how they should be utilized to achieve it.

How Does Soundproofing Foam Work?

Soundproofing foam is one of the most commonly used materials to block or absorb sound in a space. Depending on the purpose, the placement, thickness, and shape, soundproofing ability can vary.

You can use soundproof foams to keep your recording studios in an optimal sound environment. They can absorb echoes and unwanted waves from the studio and also soundproof it to some extent. Or you can also use the soundproofing foams when you simply want to block your neighbor’s loud partying.

Truth be told, there are a lot of ways to go about soundproofing foam. 

You can use it for medium-level sound blocking or layer up and pair it with other materials for complete soundproofing. It can seem confusing, but all you have to keep in mind is that you need to keep the material and the shape consistent to work it both ways.

So, soundproofing foam works by absorbing sound waves through its porous, soft surface. 

Actually, sound waves are just vibrations that are emitted from a source, like a speaker, that travel through air (mainly). This energy can either be reflected to continue their motion or absorbed with a soundproofing or acoustic material to stop their motion.  

When the sound waves travelling in a linear motion hit a hard surface, they bounce off of it, back into the room and continue their motion until they hit another surface. This creates several echoes and reverbs in the room. 

When the same hard surfaces are covered with materials such as foam and/or cloth, they absorb these waves and prevent them from reflecting.

As mentioned above, a soundproof foam can work both ways if you prioritize its shape as much as its material. 

Flat surfaces have a greater chance of bouncing sound waves off them due to their shape (plain, without ups and downs). There are fewer chances and places for sound waves to interact with the surface.

While a material or surface having more angles provides the exact opposite. Sound waves have a greater chance of getting absorbed between the “roughness” of such absorptive surfaces. 

The ups and downs from the egg crate-like surface of the soundproof foam absorb reflected sound waves from multiple directions.

These waves then dissipate all their energy into the foam and its texture before they can pass through and reach the wall behind. 

Soundproofing And Sound Absorption

Soundproofing and sound absorption are two different terms, both used for noise-reducing products. You will often hear both these terms interchangeably for soundproofing but they produce different end results.

Soundproofing means blocking sound from entering or exiting a space. 

A soundproof material will block sound by ceasing the transmission of sound waves through the material. Such soundproofing materials are dense and thick in their composition to prevent noise from penetrating in. And of course, when you can block sound from entering a room, you can block it from exiting in the same manner.

Sound absorption occurs when a porous, soft material absorbs sound waves and reduces the number of reverberations and background sounds. 

Sound absorbing material is light and porous. This allows a lot of penetration of sound waves, which is necessary for absorbing sounds.

Depending on the type of foam (shape and material), there are two main groups of soundproof foams. First is acoustic foam, which is sometimes marketed as soundproof foam, for absorption. The second is soundproof foam for real soundproofing or sound-blocking. 

Soundproof Foam For Absorbing Sound

Most soundproofing foams or acoustic foams out there don’t actually block sound. 

You will generally see these foams in the form of wall or ceiling panels of several sizes, covers, and shapes according to your needs.

Soundproof foam panels are installed onto the walls of a room at certain calculated angles to absorb sound waves coming in their direction. They can also be hung from the ceiling or put in the corners of the room if these are the areas of concern.

Acoustic foam panels should cover at least 30%-50% of the surface area for a noise-less, balanced acoustic environment.

The ideal material for this foam is polyurethane with extruded melamine foam. It has the perfect texture for entrapment and absorption of sound waves. 

When you place the soundproof foam on the walls of a room, sound waves coming their way get absorbed into it rather than passing the wall or bouncing back.

They have wedges or small pyramids on them that are molded into the side so that sound waves can hit the foams from different angles.

Soundproof Foam For Blocking Sound

Where lightweight, porous acoustic foams work to absorb unwanted reflections from a room, soundproof foams are thick and dense that block sound altogether.

The thicker, heavier, and condensed the material is, the better it is at soundproofing. These foams are closer to real soundproofing that involves preventing the sound from entering or escaping a room.

You will not necessarily find any wedges, bumps, or pyramids on these panels. Such foam is meant to be used during construction. The main purpose is to add mass and reduce air gaps to isolate sounds from one another.

They work best when installed inside the walls between layers of drywall. They not only block sound from entering and exiting but also provide insulation against heat and cold.

What’s Better?

When choosing between soundproof/acoustic foam for sound absorption and soundproof foam for sound blocking, all you have to do is define your reason.

What do you need the soundproof foam to do to your room? Make it quieter? Make it free from any and every kind of sound from outside? Make it an acoustically balanced sonic space for recording songs?

You should determine the reason for soundproofing a room both ways before you jump to the best kind of material.

If you want to lock sound inside a room or block all sound from entering it, you should get a dense, thick, and heavy soundproof foam. That too, preferably installed inside the walls of your room.

If you want to reduce the background noise or attain an echo-free space, use light and porous foam on the walls instead of inside them. Lightweight soundproofing foams will suit you best if you are content with sound absorption and moderate noise reduction.

Does Soundproofing Foam Work Both Ways?

Soundproof foam will work both ways if you install it facing both outward and inward. The foam also has to cover almost all of the surface area to work.

If you implement passive attenuation of sound in your soundproofing project, noise reduction from inside to outside will be equal to noise reduction from outside to inside. Passive attenuation means the attenuation is the same or equal from an acoustically untreated room to a treated room as it is from treated to an untreated room.

For instance, if it reduces or dampens noise coming inside a space by 35 dB, it will reduce outgoing sounds by 35 dB as well. This is regardless of how loud the source of noise gets.

Active attenuation on the other hand only operates on the noise coming from a single direction. It depends on passive attenuation and acts on the sound passing only from untreated space to the treated space. Active attenuation is also called “active noise cancellation”. Noise originating in the protected space will attenuate only to the degree of passive attenuation between the two spaces.

Let’s take another example, you soundproof a room and design it for 30 dB of noise reduction for practicing your cello. If your cello is 90 dB, you will hear about 60 dB from outside of the room. And if you play your cello outside the room, it will be heard at 60 dB by someone inside the room.

How To Soundproof A Room Both Ways?

While most of the soundproofing options will work both ways provided you take care of the mass, material, and positioning of the foam. Here are two useful ways you can soundproof a room both ways:


Decoupling is the process of separating walls and floors from each other or the structure of the building so the vibrations cannot pass through.

This includes separating each wall by suspending drywall independently from the other by separate studs. When each side of drywall is on separate studs, vibrations will transfer into one stud but won’t be able to go any further (to the other stud).

The best way of achieving complete soundproofing is to build two separate stud walls and leave a small air cavity between them for insulation. This is called a Double Stud Wall.

Another, easier option is the Staggered Stud Wall. You leave a single cavity in the wall and fill it with insulation. This option is less effective than the double stud walls because there is less mass to trap sound waves in transit.

Decoupling a wall requires access to both sides of the wall. Thus it’s only possible for you to soundproof a wall with this method if you can get to the other side. This might not be a viable option if you’re trying to soundproof an apartment wall and the loud neighbor you’re trying to get peace from is on the other side.

Adding Mass

A better solution to the decoupling problem is to consider increasing the mass on your side of the wall. This will thicken the barrier between the two rooms and make it harder for sound waves to pass through from each side.

Two great products for this purpose are mass-loaded vinyl and drywall. You can stuff any wall cavities with materials like fiberglass or wool but mass-loaded vinyl and drywall are the best products for the mass.

Any mass-adding product is easy to attach to your existing wall. All you have to do is seal the edges with acoustic caulk and work your way around sockets and vents in the room.

This will add bulk to your wall, you can also always layer it up with another layer if it isn’t taking too much space in your room. The limp mass of mass-loaded vinyl helps with sound dissipation at a faster rate and effectively blocks noise from entering or exiting the room.

You can use both of these products for the best results. Add a layer of mass-loaded vinyl and cover it up with drywall.


Can soundproof foam work both ways to stop noise transmission?

Yes, they definitely can work both ways. Almost all kinds of soundproofing foams provide a certain degree of soundproofing but some options are more effective than others.

You can either soundproof your walls during construction or re-do them later if you’re aiming for a serious sound-blocking job. Options are somewhat restricted when it comes to complete soundproofing of a wall post-construction, but the best hack is to add mass. More mass equals less sound transmission.

In a more real sense, it all depends upon the reason you want your soundproof foam to work for incoming and outgoing noise. Furthermore, for a soundproof foam to work both ways and fully mute noise incoming from the outside or outgoing, it has to be dense and thick.

A light and soft soundproof foam will help more with controlling vibrations, echoes, and reverberation from the room, it won’t completely dampen sound going out or coming in.

Whatever option and kind of soundproof foam you choose, installing a soundproof foam in your room will drastically improve the sound quality. A soundproof foam working both ways is a cherry on top!