Flexible Polyurethane Foam Applications
Sound Insulation
And Absorption
Flexible polyurethane foam (FPF) is frequently used for sound insulation and sound absorption. The open cells in the foam and its flexible surface absorb and dissipate sound waves. Instead of bouncing off hard surfaces and creating echo or cancellation effects, much of the sound energy is absorbed by the foam.
The result is a quieter, more controlled acoustic environment.
Top: Sound absorption panels made from flexible polyurethane foam are often fabricated into shapes with peaks and valleys to deflect sound energy and dampen its effect. Panel designs may differ, depending on the type of sound the user wants to control.
Left: Sound absorption foam is often used in audio editing suites so operators can focus on particular sound characteristics.
Flexible polyurethane foam's sound deadening qualities can be applied in a variety of uses.
Foam is a very common sound insulation material in many applications. Among these are:
Recording Studios. FPF’s ability to dissipate sound waves and reduce echoes make it a frequent choice for these applications. Carefully-placed foam panels can actually "shape" the acoustics of a room to match its intended uses.
Building Noise Reduction. Foam for sound insulation can be placed behind drywall to reduce noise, especially in highly occupied apartments or offices. Decorative panels containing foam may be used in large open areas to reduce echo effects and make spaces more inviting. Carpet cushion, a very common use of foam, reduces noise from foot traffic and other activities, makes the carpet more comfortable and durable.
Automotive And Other Transportation. The automotive industry uses foam in vehicles to reduce noise from engines, tire and road noises, and vibration from motion. These materials are called "NVH" (Noise, Vibration, Harshness, and are part of almost all vehicles. Aircraft builders also use FPF to limit NVH in aircraft interiors. Foam used in auto and aircraft interiors is often required to meet certain federal flammability regulations. See our InTouch bulletin on Transportation.
Machinery. Noise and vibrations from industrial machines can be extreme. Flexible polyurethane foam can help reduce noise to manageable levels, and reduce vibration that may cause equipment damage.
As foam became more prevalent in sound insulation, foam manufacturers and fabricators created a spectrum of specialty foam grades and shapes to optimize its sound reduction properties.
The Science Of Sound Management
Above: Depiction of sound waves traveling through a room.
To understand sound insulation, you first must understand sound. Sound is basically the vibration of energy.
Above: Sound waves bounce off hard surfaces (acoustic reflection). This creates echoes and distortion.
Below: Sound waves also bounce off each other. Depending on how they contact they may amplify each other--or cancel each other out.
When something vibrates (e.g., two objects hitting each other, a dog barking), the surrounding air also vibrates. These vibrations carry through the air as waves.
Sound waves transfer the vibration from the air to your ear structures, which vibrate in turn, and this sensation is recognized by your brain as noise, music, or speech.
Sound waves are dynamic—they move around a room, hitting walls and bouncing off.
If the room is big enough, these bounces create an echo effect, and because the bounces can re-shape the waves, the sound may be distorted in other ways.
Sound waves can also bounce off each other. Depending on how they collide, they can even cancel each other out. Waves are made up of peaks and troughs. If the waves meet peak-to-trough, the wave is flattened and no sound occurs. If they meet peak-to-peak, the sound may be amplified.
All of these phenomena can cause audio problems. When a roomful of people are talking, multiple waves from multiple sources bounce around and become muddied by the interaction. This can create an unintelligible din.
Over time, it was discovered that different materials could have different effects on sound wave. Hard surfaces allow the waves to bounce freely, while soft surfaces can deflect and absorb the wave energy, change its properties, or even remove the impact of the sound. This is done by converting the energy of the sound waves to heat, as they impact the soft, porous surface of the foam and dissipate instead of reverberate.
Sound engineers also learned that changes in the shape of soft materials can be used to "shape" the sound of a room. Ridges on foam may absorb part of the sound energy, but not all.
When sound waves contact foam used for acoustic insulation, their energy is absorbed and converted, changing the sound dynamics for the entire space.
The Difference Between Sound Absorption And Soundproofing
There is sometimes confusion between two common terms in sound management: Soundproofing and sound absorption.
Soundproofing's purpose is to prevent sound from entering or leaving a space. This is done by using heavy, dense materials, which block sound. For soundproofing, small cracks and openings must also be blocked, because sound can travel through them. For these reasons, rigid foam products are often used. For example, rigid spray foam insulation may be used to fill in gaps or holes.
Sound absorption, on the other hand, is used to improve the acoustic quality within a space by reducing echo and reverberation. Flexible polyurethane foam is the choice here.
Light, porous foams trap and modify sound waves. Foams may be fabricated into ridges or points to deflect sound or negate it. In recording studios and rehearsal spaces, flexible foam “traps” can be used in room corners to keep deep bass notes from distorting, and using ridges to break up harsh reflections.
How FPF Is Used In Sound Absorption Applications
Fabricated Foam Sheets Or Tiles. These are often used in sound studios, because they are easy to install, can be repositioned if needed, and are typically affordable. There are numerous companies that produce specialized foam for sound absorption, many of which have been carefully designed for specific performance properties.
Decorative Panels containing flexible polyurethane foam. Foam is encased in fabric or other material, but can still provide sound absorption properties. Panels are often used in large open spaces where echoes can be distracting, but they may also be used in smaller rooms for decor and a quieter, more comfortable environment.
Bonded Foam Carpet Cushion. Carpet cushion is a common residential use of foam for sound absorption and more comfort underfoot. Bonded foam is made from recycled post-industrial and post-consumer scrap, and provides a high performance product to protect carpet and increase its life. Foam recycling into bonded foam is also a sustainability success story. See our InTouch bulletin on Carpet Cushion.
Molded And Slabstock Foam. FPF is used to control NVH (Noise, Vibration, and Harshness) issues. A key to controlling vibration is to lower the foam resonance to a frequency below the critical human discomfort level, while avoiding the natural frequencies of the vehicle. For these uses, both molded foams (shaped to fit a compartment) or slabstock foams (blocks or sheets) are used. Even small amounts of foam in the right places minimize squeaks, creaks, and rattles. See our Transportation InTouch bulletin.
Characteristics And Properties Of Foam For Sound Absorption
It typically isn't necessary to cover an entire room in foam panels for sound absorption. Strategically placed panels will often provide the performance needed.
Sound engineering can be complicated, and for professional installations, it is wise to consult a specialist. For many room applications using foam for sound absorption, it is not necessary to put foam on all surfaces. Often, strategically placed foam materials on a fraction of the surface area will provide the sound properties desired.
A specialist can also advise you on particular shapes and grades of foam (considering factors like foam density and softness) that will provide the best acoustic performance.
It is also important that the flexible polyurethane foam used meets the proper fire safety standards and building codes for the application. Use in public spaces in particular may call for relatively stringent fire safety standards, such ASTM E84 / UL 723, which measure the surface burning characteristics of building materials. Foam labelled as complying with 16 CFR Part 1640 or TB-117-2013 is designed to resist smoldering ignition of upholstered furniture, and is not relevant for foam used in acoustic applications.
Related Resources
Related
Video: Foam Applications
Learn more about flexible polyurethane foam in furniture, bedding, automotive, flooring, packaging, and other uses.
Video: Foam Chemistry
Detailed information about the many variables in foam chemistry and how different formulations affect foam properties.
Flexible Polyurethane Foam: A Primer
How FPF is made, specified and used in different applications.
Technical: Foam Fabrication
The processes for creating custom shapes of flexible polyurethane foam
Technical: Molded Foam
Foam manufactured within a shaped form, often used in transporation applications.
Technical: Carpet Cushion
How foam is used to make rooms quieter and make carpet last longer.
Technical: Transportation
How foam improves comfort and reduces noise and vibration in vehicles.