Closed cell foam is not a good choice for most soundproofing goals. Its rigid, sealed structure reflects sound waves rather than absorbing them, which makes it far less effective than open cell foam, fiberglass, or dedicated soundproofing materials. That said, closed cell foam does have a few narrow acoustic uses worth understanding, especially if you’re already planning to install it for insulation.
Why Closed Cell Foam Struggles With Sound
Sound absorption works by letting sound waves enter a material and lose energy as they pass through it. Open cell foam does this well because its tiny interconnected bubbles act like a sponge, creating friction that converts sound energy into small amounts of heat. Closed cell foam does the opposite. Its cells are sealed shut and filled with gas, creating a dense, rigid surface that bounces sound waves back instead of letting them in.
This is the core problem. Closed cell foam is typically 1.7 to 2.6 pounds per cubic foot, roughly three to four times denser than open cell foam (which sits around 0.5 pounds per cubic foot). That density is great for structural strength and moisture resistance, but it works against sound absorption. A wall filled with closed cell spray foam will do very little to reduce echo or reverberation inside a room, because the sound just reflects off the material’s surface.
How It Performs in Wall Assemblies
Testing by the Insulation Institute on standard wood-stud wall assemblies found that a full cavity of closed cell spray foam achieved an STC (Sound Transmission Class) rating of 31. That’s a modest score. For context, normal conversation is clearly audible through an STC-31 wall. Loud speech is easily understood. An STC of 45 or higher is generally considered the minimum for reasonable privacy between rooms.
Adding a layer of fiberglass batt insulation behind a 1-inch “flash” coat of closed cell foam bumped the rating to STC 34, a small improvement. But the same testing showed minimal variation between insulation types overall, with differences of 3 STC points or less. In other words, closed cell foam performs about the same as other common insulation materials when it comes to blocking sound through a wall, and none of them perform well enough on their own for serious soundproofing.
Compare that to mass loaded vinyl, a purpose-built sound barrier that adds 20 to 30 STC points to a wall assembly at just 1 pound per square foot. If your primary goal is blocking noise between rooms, dedicated soundproofing products will dramatically outperform any type of foam insulation.
Where Closed Cell Foam Actually Helps
Closed cell foam does seal air gaps extremely well, and air gaps are one of the biggest pathways for sound to travel between spaces. If you have a drafty wall or ceiling where sound leaks through cracks, gaps around outlets, or openings around pipes, closed cell foam will plug those paths. This won’t turn a wall into a soundproof barrier, but eliminating air leaks can make a noticeable difference, especially for high-pitched sounds like voices or music.
The material also has legitimate uses for vibration damping. In vehicles, appliances, and industrial equipment, closed cell foam pads are placed between metal panels and frames to prevent rattling and buzzing. It works well in this role because the dense, slightly flexible material absorbs mechanical vibrations before they can transfer to surrounding surfaces. This is why you’ll find closed cell foam inside car doors, box trucks, horse trailers, and machine housings. In the automotive industry, it serves as an acoustic insulator that dampens engine noise, wind noise, and panel vibrations.
These are specific, targeted applications. They’re not the same as soundproofing a home theater or bedroom wall.
Open Cell Foam Is Better for Noise Reduction
If you’re choosing between spray foam types and noise is a concern, open cell foam is the stronger option for acoustic performance. Its soft, porous structure absorbs airborne noise like voices, television audio, and music. It’s particularly effective at mid- to high-frequency sounds, which are exactly the types of noise that travel most easily between rooms in a house.
Open cell foam is also the better pick for dedicated listening spaces. In a home theater, for example, you want the walls to absorb sound inside the room to reduce echo and improve audio clarity. Closed cell foam would reflect that sound back, creating muddiness and reverberation. Open cell foam dampens those reflections.
The tradeoff is that open cell foam doesn’t provide a vapor barrier, has lower structural strength, and offers less thermal insulation per inch. So the choice often comes down to priorities. If you need moisture resistance, structural rigidity, and thermal performance (exterior walls, basements, crawl spaces), closed cell foam is the right call for those reasons, and you’ll get a small acoustic benefit from air sealing. If noise reduction is the driving concern, open cell foam or a dedicated acoustic product will serve you far better.
What Actually Works for Soundproofing
Effective soundproofing relies on mass, decoupling, and absorption working together. No single material does all three. A high-performing soundproof wall typically combines heavy drywall (sometimes doubled), a decoupling system like resilient channel or staggered studs that prevents vibrations from transferring through the frame, and cavity insulation that absorbs sound energy inside the wall.
Closed cell foam can contribute to one piece of that puzzle by sealing air leaks, but it won’t replace any of the other components. If you’re already installing closed cell foam for insulation and hoping it doubles as soundproofing, expect only a marginal acoustic benefit. If soundproofing is the goal, your budget is better spent on mass loaded vinyl, acoustic drywall, or decoupling hardware than on upgrading your foam type.