Spray foam is easy to install, relatively inexpensive, and highly effective at sealing and thermally insulating walls. It’s no surprise then, that soundproofing with spray foam insulation is such a commonly asked question.
Spray foam insulation does marginally reduce noise (open-cell type) but it’s not nearly as effective as other materials like mineral wool and fiberglass. In addition, spray foam can help reduce sound by expanding and filling inaccessible air gaps that would otherwise transfer noise into or out of a room.
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Can Spray Foam Reduce Noise?
The answer to this question depends on two things:
- The type of spray foam insulation.
- The NRC (Noise Reduction Coefficient) of the foam.
Open Cell vs Closed Cell
While there are dozens of polyurethane foam formulations on the market, they can all be classified into 2 types – Open Cell and Closed Cell insulation.
- Open Cell foam has an open structure when expanded, similar to a sponge, and is typically softer and more flexible than closed cell.
- Closed Cell foam has a rigid closed structure when expanded. There is no path for moisture or ait to escape. These properties make them excellent choices for thermal insulation.
Mass, Dampening, and Isolation are the so-called “3 legs” of the noise reduction stool. To reduce noise, soundproofing insulation has to be effective in each of those areas.
Let’s look at how the two types of spray foam stack up:
Mass – The more mass, the more noise and sound vibrations can be absorbed.
- Spray foam insulation is not very dense and not a good deadener. A density of 1-3lb/cubic foot is common and is just a fraction of the density of fiberglass panels or mineral wool sound batts (6-8lb/cubic foot).
Dampening – Think of this like shock absorbers, dampening smooths out bumps in the road (or big sound waves in this case).
- Closed-cell formulations are too rigid and do not perform well in dampening sound. Rigid foam has little “give” when sound waves hit, so they transmit through the material rather than dissipate.
- Open-cell spray does have some dampening properties, as it’s somewhat softer and more flexible to allow sound to dissipate within the foam structure.
Isolation – By decoupling a wall cavity or ceiling, it is being isolated from the other side, making a sound barrier reducing noise transferred in or out of the room.
- Closed-cell spray foam is more rigid and does not isolate very well. Spray foam expands and seals wall stud cavities, which is great for thermal insulation but tends to couple the wall (transmitting sound) rather than isolate it from noise.
- Open-cell spray foam is more spongy and has more damping ability, and therefore isolates better in the wall cavity than closed-cell foam.
The Bottom Line?
Spray foam should not be the first choice when it comes to soundproofing your wall, there are much better options like fiberglass and mineral wool.
Spray foam CAN be used effectively to fill and seal up cracks and air gaps that are pathways for sound.
If you decide you still want to use spray foam in your project, be sure to use open-cell spray foam. Open-cell foam is usually more flexible, allowing sound waves to penetrate and dissipate.
Spray Foam NRC
When talking about noise reduction/sound absorption of spray foam insulation, you also need to look at the NRC (Noise Reduction Coefficient) rating of the material. And then the STC (Sound Transmission Class) rating of the combined materials used in the wall assembly, which we’ll get to later.
The NRC rating is on a scale of 0.0 to 1.00. In simple terms, an NRC of 0.8 would mean the material absorbs 80% of noise while reflecting the remaining 20%.
- 3 inches of open-cell spray foam has an NRC of approximately 0.70 (this depends highly on the foam product), which is comparable to just 1.0” of rigid fiberglass.
- Closed-cell foams have an NRC of approximately 0.20, meaning it absorbs just 20% of the sound directed at them while reflecting the other 80%. Not very good, is it?
Just 2 inches of fiberglass or rock wool sound insulation easily surpasses open-cell spray foam in sound absorption and noise reduction, with NRC ratings in the 0.95-1.00 range.
Soundproofing with Spray Foam Insulation
According to Johns Mansfield and NAIMA, a standard 2″x4″ wood stud wall with 1/2-in gypsum boards, you will have near identical soundproofing ability between plain R-13 fiberglass or open-cell spray foam. The STC rating for both is 38.
In another study by the Insulation Institute, they tested walls constructed of 2″x4″ wood stud walls with ½” Gypsum on the interior side, and OSB sheathing, Tyvek wrap, and Vinyl Siding on the exterior.
Each test utilized a different type of insulation and measured the STC and OITC. Recall that OITC is equivalent to STC but from outside noise.
| Insulation | STC | OITC |
|---|---|---|
| R-13 Fiberglass Batt | 33 | 25 |
| R-15 Fiberglass Batt | 34 | 25 |
| R-15 Mineral Wool Batt | 34 | 25 |
| Open Cell Spray Foam | 33 | 25 |
| Closed Cell Spray Foam | 31 | 24 |
| R-13 Fiberglass Batt + 1" Open Cell SPF | 34 | 26 |
| R-13 Fiberglass Batt + 1" Closed Cell SPF | 34 | 25 |
Takeaways
- There is no soundproofing advantage to using spray foam over regular fiberglass batt insulation.
- Spray foam might have comparable STC and OITC ratings to fiberglass and mineral wool but is more deficient at blocking lower frequency sound.
- Open-cell spray foam has superior soundproofing abilities to closed-cell foam insulation.
- If you do use spray foam insulation, the combination of batt insulation and spray foam insulation will achieve the best soundproofing results.
- A 2″x6″ wood stud wall, with half fiberglass or mineral wool and half spray foam will have excellent soundproofing and STC ratings.
- The added mass of two layers of gypsum panels with a viscoelastic polymer bond (Green Glue), greatly enhances the STC of any wall construction.
Best Spray Foam for Soundproofing
For filling gaps, choose a foam that is designed for sealing up windows and doors. You’ll get better fill and adhesions with blends designed for this application. We like DAP Barrier Multi-Purpose, Loctite TITE FOAM Window & Door, and .
- All seasons formula blocks drafts, water, fire and pests
For spraying your walls, we’d recommend the DAP Touch ’N Seal Professional 2 part polyurethane kit. It’s designed for use in walls, ceiling joists, attics, and more.
- ASTM E-84 Class A Fire Resistance,
- Reduces energy loss by as much as 40% and Reduces sound transmission
- Does not shrink or settle like cellulose, Maintains air seal, and Significantly increases structural
Yes, it’s closed-cell, the stuff we said isn’t the best for soundproofing. It’s terribly difficult to find commercially available open-cell spray foam. You’ll have to work with a contractor in most cases to get it.
This kit is professional grade stuff, so make sure you have all the proper dispensing and safety gear or you’re gonna have a bad time.
Can You Soundproof Existing Walls with Spray Foam?
There are two ways to shore up the soundproofing on existing walls.
Method 1 is to inject it behind door and window frames, and gaps created by pipes or beams. The foam expands into gaps where noise can infiltrate.
- Carefully pry off the door & window frame material.
- Look into the wall, looking for air cavities between the last stud and the drywall.
- Inject spray foam insulation in all the spaces, then cut off any excess.
- Reattach the frame pieces and paint or finish as necessary.
Method 2 is to inject liquid foam down wall cavities, even if there is already insulation in place. The foam reacts and expands upward filling the available space between gypsum, studs, and batts.
- Using a spade bit or hole saw, drill into the wall between each stud near the ceiling.
- Inject the liquid foam compound downward towards the floor.
- Listen for the expansion of the foam before stopping, watching for excess foam expanding out the holes.
- Cut off any excess cured foam and cover the holes with sound-absorbing panels.
Can You Soundproof a Door with Spray Foam?
Yes, there are methods for soundproofing a hollow core door with expanding foam spray insulation.
The benefits are a reduction of 4-5 dB of sound transmission through your door.
Spray foam is just one of many tactics for reducing sound coming through your doors.
How do you do it? Here’s the general process:
- Determine the composition of your door, locating any dividers or cores inside the door skins. Mark an X on the edge of the door, marking the centers of each section. Do this along all four sides of the door.
- Drill a ¼ inch hole at each X mark, and another hole approximately 12 inches next to it. These are the foam spray fill and exhaust locations.
- Carefully insert the straw into one of the holes and slowly start spraying in the foam. Once you see the foam expanding out the exhaust hole, stop immediately.
- Repeat this process until all sections of the door have been filled, and allow the foam to cure.
- Remove any excess foam from the edge of the door with a sharp knife. Fill, sand, and paint or stain over the holes to match your door.
Here is a video version of this process.
Conclusion
While spray foam can reduce some noise, it’s only as good as regular fiberglass. There are indeed ways to soundproof with spray foam insulation, and we hope you can utilize what you’ve learned here to reduce noise in your home.
*Last updated 2024-09-08 at 22:53 / Product Links & Images from Amazon Product Advertising API
