Best by project · Based on the 2021 IRC; your local code may differ
Foam seals the air paths. It does not add mass, and mass is what stops sound.
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Two different problems get sold under the word soundproofing. One is noise leaking through openings: the gap under a door, an unsealed outlet box, a duct that runs from one room into the next, a hole cut for a pipe. The other is sound going through the assembly itself, wall, floor or ceiling, where there is no hole at all. Foam is genuinely good at the first and modest at the second, and almost every product claim you will read blurs the two.
One product in our whole set publishes a sound figure tied to a test method; TYTAN prints 62 dB with no method named. The HandiFoam Low Density sheet, revision 6/2024, prints STC 35 in a stud wall with 3 in of foam and NRC 0.70 at 3 in, and describes the product as designed to "deaden sound or reduce vibration." It names the assembly type and the thickness, which is more than anyone else gives, though it does not name the test report. Against that: TYTAN states "62 dB sound-blocking" with no standard, no assembly and no test named, and a row of kits carry "heat and sound insulation" in the listing title with nothing at all behind it. That gap is the whole story of this category.
Assembly, moisture and code planning for this job is at our sister publication under common ownership: Insulation and sound-control evidence, at Spray Foam Guides. This page stays with exact products and the records their makers publish.
The assembly decides the product
Sound transmission class comes from testing a whole assembly to ASTM E90 and rating it to ASTM E413. It is a property of the wall that was built, not of any one material in it. HandiFoam prints STC 35 in "a stud wall," and the sheet does not give the stud size, the spacing or what was on each face, so there is no way to separate what the foam contributed from what the wall would have done empty. That is not a criticism of the number. It is what an STC number is.
Noise reduction coefficient measures how much sound a surface absorbs rather than reflects. It is about echo and liveliness inside one room, not about what your neighbor hears. NRC 0.70 at 3 in is a real absorption figure and it is irrelevant to whether the television next door keeps you awake. The two get quoted together constantly and they are not the same claim.
Open cell foam is soft and porous, which is what absorption inside a cavity needs. Closed cell is not, and the reason it does little for sound is not that it bridges the two faces: in an ordinary single-stud wall the studs already do that, and that path dominates. It is that a rigid, closed fill absorbs poorly and stiffens the air in the cavity, so measured results put it at or barely above an empty cavity while fibrous or open-cell fill does better. The only sound figures anywhere in our set belong to the open cell sheet, and among the products we tracked as of September 8, 2026, the only open cell ones are the two-component kits.
What the code says
Section numbers are from the 2021 International Residential Code. Your city or county adopts one edition of the code and changes parts of it, and your local building official has the final word. A thermal barrier and an ignition barrier are different things, and the glossary explains both.
Products that document this job
Listed by product family. Each line says why the product is on this list, always from something the maker published. Follow the link for the documents, the questions still open, and dated prices.
Quantity, worked once
Board feet are square feet times inches. The kit figures are the makers’ theoretical yields, which every maker that defines the term says are laboratory numbers; plan on less.
One II-450 kit covers it on the maker figure, and what you buy is the STC 35 the sheet names for its own test wall. That sheet also says professional use only and names a powered air purifying respirator, which is worth pricing in. Before spending it, seal the outlet boxes and the top plate, because an unsealed box will undo more than the foam adds. If the wall is open and quiet is the actual goal, price a second layer of board against the kit and compare.
Run your own numbers in the calculatorQuestions
It seals it, which is not the same thing and is often more useful. Air paths carry noise directly, and foam closes them. What it does not do is add mass to the assembly, and mass is what stops airborne sound going through a wall that has no holes in it. The one published figure in our set is STC 35 for an open cell foam in a stud wall at 3 in, and STC 35 is a modest number for a partition.
Open cell, on the evidence. It is soft and porous, which is what sound absorption needs, and it is the only cell type with a published figure in our set. Closed cell is rigid, and a rigid fill couples the two faces of a partition rather than isolating them. If a listing sells closed cell foam on a sound claim, ask what standard the claim was measured to.
Three things, in this order. Seal every opening, which is where foam earns its place. Add mass, usually a second layer of board. Then decouple, so the two faces of the wall do not share the same studs, using staggered studs, a double wall, resilient channel or isolation clips. A damping compound between two layers of board adds to that. Cavity absorption belongs with them rather than instead of them: it does little on its own in a single-stud wall and a lot inside a decoupled one.
From the job to the finished wall
This page answers it for sound control. The same five questions run for every other part of the house.
Board feet are the area times the thickness. Price the kits that cover them against hiring the job out.
A kit, the gun and cleaner it works with, something to cover what stays clean, and the gear you wear.
Check the temperature, prepare the surface, spray in passes and cover the foam where people live.
The sheets give a tack-free time in minutes and a full cure in hours; only some say when people can go back in.
We have not sprayed or tested any product on this page, and nothing here stands in for the label, the safety data sheet or what your local inspector tells you.
