When soundproofing my home office and my son’s band practice space, I wanted to know “does spray foam insulation reduce noise?” I checked out open and closed cell spray polyurethane foams (SPF) to see if I could use it for thermal and acoustic insulation.
Does spray foam insulation reduce noise? Based on my research, the easy answer is no. Open cell spray foam performs better than closed cell, but neither is effective at blocking sound transfer. The qualities that make it an excellent thermal barrier also create disruptive resonance and its adhesion couples the wall elements together increasing noise transfer.
Some of my friends and clients expressed an interest in what I was doing, so I figured I’d share my findings. Hope they assist you in controlling noise intrusion in your home or office.
What is Spray Foam Insulation?
Spray foam is an open or closed cell polyurethane material that is made of two components that mix when sprayed onto walls or into wall cavities. It expands to cover a surface or fill a crevasse or cavity before hardening.
One part of the liquid spray is polymeric MDI (methylene diphenyl diisocyanate), and the other is a blend of polyol resins, fire-retardants, surfactants, and catalysts. The fire retardants decrease the combustibility and smoke generation.
Closed cell spray foam expands between 35 and 50 times its original volume and weighs about 2 lb/ft³ when hardened. An ozone friendly hydrofluorocarbon is commonly used to deliver the mixture to the wall surface or cavity where it expands and hardens.
Over 90% of the cells are closed making the foam impermeable to moisture and vapor, and improving its thermal values. It has an R-value of 6.1 per inch of thickness. The hardened polyurethane has a tensile strength of 28psi and is much less compressible or flexible.
The greater strength offers advantages in hurricane or earthquake prone areas to help secure wall and roof components together.
Open cell polyurethane foam expands to 150 times its original volume and weighs about 1/2 lb/ft³. Water is used to drive the blended materials onto the wall or into a cavity where it expands to form an open-celled matrix that remains slightly compressible and flexible.
The interconnected open cells trap airflow making it a good thermal barrier. It blocks air flow and has a thermal R-value of 3.6 per inch, but is semi-permeable to moisture and vapor. It has a tensile strength of 4.0psi.
Airborne and Impact Noises
There are several types of noises we try to control in our homes or offices. Airborne and impact sounds are the two we normally attempt to control with insulation. Soundwaves are vibrations that travel through the air until they encounter an obstacle – wall, tree, window, person, etc. The frequency wave vibrates its way through the object and continues.
Some of the waves may be absorbed or reflected, so less travels onward, which can reduce the intensity of the sound. The barriers don’t usually work on all frequencies, absorbing some but not others.
Low frequency sounds from drums, and bass instruments take a lot to decrease. We’ve all felt them reverberate through walls and vehicles. Mid-range and high frequencies tend to be easier to mute.
Impact noises occur when something hits a surface inside or outside a structure. They are also known as structural sounds. Foot-falls on hardwood or concrete can echo through a building.
Bouncing a tennis ball or basketball against the wall or even on the driveway reverberates into the building the same way. The impact initiates the airborne vibration through a barrier into another space within your home or office.
What Do The Sound Ratings Mean?
The sounds we hear usually range from 20 to 20,000 Hz; age and other issues factor into the range we hear too. 0 decibels is essentially silence. The rustle of leaves is between 10 and 20 dB, a quiet home or office is 40 dB, and the average street noise or a party between 75 and 80 dB. A bass drum, jet engine or car horn can be an ear-splitting 130 dB.
Hertz (Hz) is used to measure frequencies of sound waves, and decibels the loudness heard or intensity produced by different sounds. The STC measures how different materials or barriers interact with 16 different frequencies. The NRC how much sound intensity they block.
Sound Transmission Class (STC)
The STC is a value used to rate how effective different materials or combinations of materials are at improving the sound transmission loss (TL) in decibels (dB). It rates the movement of 16 common frequencies between 125 Hz and 4,000 Hz through the materials or assemblies. The less sound measured going through, means the greater the transmission loss, and the higher the numeric STC rating.
Noise Reduction Coefficient (NRC)
The NRC is a number system used to rate how well a tested material absorbs or reflects soundwaves. It represents the average tested absorption results of four common frequency ranges – 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz.
The average is the NRC value and is rounded to the nearest 0.05 between 0 and 1.0. The greater the value, the better the material is at absorbing or reflecting sound.
Does Spray Foam Insulation Reduce Noise?
To soundproof a partition wall, consider the structure and weight of the material you want to use. We know we need to absorb, block, and damp the sound waves, plus decouple the layers to stop sound transfer through the wall. Some materials have NRC and STC ratings that help us out, and you can read about it in my post about soundproofing insulation options.
When we apply what we know about open and closed cell polyurethane we can also understand why it may not be good for soundproofing. Although it has good thermal properties, it doesn’t have the mass to absorb soundwaves.
The hardened foam forms a rigid material that also interferes with absorption. Couple the harder material with open or closed cells, and you get increased resonance whereas a softer more airy substance will damp it.
The property that makes the spray foam good for hurricane and earthquake zones is also what makes it bad for decoupling. It secures wall components together, so that sound vibrations can move through more easily. The wall construction, the thickness of the foam, and wall sheathing influence performance too.
Comparison of How Insulation Improves the STC Rating of a 2”x4” partition wall with 1/2″ drywall on both sides and an initial STC between 33 and 35
|Open Cell Polyurethane
|Closed Cell Polyurethane
|Rockwool Safe’n’Sound Batten
|Owen-Corning R-11 Batten
|Owen-Corning Fiberglass 703
As you can see from the comparison table, spray foam is not the best material for sound insulation. Closed cell spray foam insulation has the lowest noise deadening ratings.
Open cell polyurethane spray foam performs better with noise reduction and comparable to fiberglass batten insulation. Both types of foam largely underperform compared to Rockwool and fiberglass rigid insulation.
Although the values should indicate an improvement in the sound attenuation of a standard 2×4 partition wall, the adhesion of the foam to the components allows soundwaves to pass through easily.
Additionally, the open and closed cells in the hardened foam increase mid-range frequency resonance distorting the sound quality. It has excellent thermal performance, but comparatively not a good soundproofing material.
Spray Foam Insulation CostOpen cell polyurethane spray foam is less expensive than closed cell. The cost of the material depends on where you live, and if you plan to install it or have the pros. Some places give the cost per board foot and others by square foot at R-1. However, I prefer a 1-inch thick square foot price.
Polyurethane Foam Insulation Cost
(Not including labor)
|Cost per Board Foot
|Cost per Square Foot at R-1
|Cost by Square Foot 1”x12”x12”
|Open Cell Polyurethane Foam
|$0.40 – $0.75
|$1.00 – $1.20
|Closed Cell Polyurethane Foam
|$1.00 – $1.50
|$1.25 – $1.50
Better Alternatives for Soundproofing
There are alternative insulation products that can be used instead of polyurethane spray foams. They have excellent thermal properties like the foam but have even better soundproofing abilities.
Retrofit:Trying to improve the soundproofing of existing walls can be a challenge. Blown in cellulose insulation is 75-85% recycled material and is an excellent sound absorbing material that reduces feedback, and mutes echo.
It comes in two formats – loose fill which is less expensive, and dense fill. Loose fill has an STC of 44 and an NRC of 0.80, while the dense fill has an NRC of 0.90 and STC between 44 and 68 depending on how dense it’s packed.
New construction offers a blank slate for soundproofing. Metal or wood studs, isolation clips and channels to decouple layers, mass loaded vinyl, Green Glue for damping, newer construction techniques, and your choice of insulation.
It’s easier to soundproof from the start than to retrofit sound control in later. Two helpful articles you may find interesting are How to Soundproof Walls and Soundproof a Basement Ceiling.
Fiberglass battens and panels insulate and also soundproof more effectively than foam. Owens Corning 703 Fiberglass Panels are 2-inches thick and have an NRC of 1.10 and an STC of 52. The panels can be used on the wall or inside the cavities. It absorbs sound, reduces echo, and control reverberation.
- Stone Wool
Stone wool is available in insulating boards and battens too and is also better for controlling sound than the spray foams. mineral wool insulation is 2-inches thick, has an STC of 52, and an NRC of 1.10. Like fiberglass, it reduces echo, controls reverberation, and absorbs sound.
Polyurethane spray foam is great thermal insulation and it does have some soundproofing potential. Unfortunately, the characteristics that allow it to trap soundwaves also create a resonating chamber that seems to amplify mid-range frequencies which are disruptive.
Additionally, the hardened foam also binds layers together which couples the wall elements and can increase sound transfer. If you found this article of interest and you know someone who might appreciate it, pass it on. Your comments and suggestions are appreciated too.