Cellulose is the gray, shredded-paper-looking material a contractor blows into an attic floor or packs into a wall cavity. It insulates at roughly R-3.5 per inch. It’s made mostly of recycled newsprint, and it’s manufactured to ASTM C739, the spec covering what goes into it, how it performs, and how it has to behave in a fire.
The question usually comes up mid-quote on a retrofit, when it turns up as a third option next to fiberglass batts and spray foam and nobody bothers to explain the difference.
It’s not a fringe product, either. The U.S. cellulose fiber insulation segment generated $415.5 million in revenue in 2024, according to Global Market Insights, which makes it the largest natural fiber category in the country’s insulation market.
What Is Cellulose Insulation?
It shows up on the job in compressed bags as loose fiber, not as a pre-cut blanket. Installers blow it in. Loose into an open attic, or packed tight into a closed wall, and either way it fills the cavity without seams.
That seamlessness is most of the pitch. Batts come in fixed widths. Cavities rarely cooperate.
It sits inside the broader category of home insulation, meaning anything installed to slow heat moving between the inside and outside of a house. Building codes rate it on the same R-value scale as fiberglass and mineral wool, so comparisons are at least apples to apples.
Paper-based fill also has a longer history than the “green alternative” framing suggests. Thomas Jefferson’s Monticello was insulated with an early cellulose-like material in 1772, a detail building historians tend to bring up whenever someone calls the stuff new.
A few things it isn’t, because these come up constantly:
- It’s not a vapor barrier, though it’s often paired with one
- Nothing structural about it. It carries no load
- And it has no relationship to the vermiculite or asbestos-based fill sitting in some pre-1980s attics
That last one matters more than it sounds. Gray fiber in an old attic makes people nervous, and reasonably so. Worth knowing how to tell the difference between cellulose and asbestos insulation before anyone starts disturbing it.
What Is Cellulose Insulation Made Of?
Old newspapers, mostly. Cardboard too. The paper gets milled down to fine fiber and coated with a fire retardant, and that’s the product.
The recycled share isn’t a marketing number. Federal purchasing rules under the EPA’s Comprehensive Procurement Guidelines set a minimum of 75 percent post-consumer recycled content for cellulose insulation, and CIMA member manufacturers commonly report 85 percent or higher (Cellulose Insulation Manufacturers Association, 2025).
The recipe is short:
- Recycled newsprint and cardboard, which form the base fiber
- Boric acid, doing fire and pest duty at once
- Ammonium sulfate, used as an alternative or as a secondary retardant
Those additives run around 15 percent of total weight, and they’re carrying more of the product than people expect. Fire class and pest resistance come from the treatment. The paper is just paper.
Greenfiber, formed out of the 2022 merger of Applegate and Greenfiber, now runs the largest cellulose production network in North America and pulls most of its fiber from post-consumer newsprint.
What Types of Cellulose Insulation Are There?
The product splits along installation method rather than chemistry. Roughly the same fiber, handled differently depending on where it’s going.
| Type | What It Is | Typical Use |
|---|---|---|
| Dry cellulose | Loose fiber blown without water or adhesive | Open attics and enclosed walls |
| Spray-applied | Fiber mixed with water and adhesive on site | Open wall cavities before drywall |
| Stabilized | Dry fiber bonded with a light adhesive mist | Flat attic floors needing extra hold |
| Low-dust | Fiber treated to cut airborne particles | Homes with dust-sensitive occupants |
Dry cellulose is what most homeowners actually get, and it covers two installation approaches that look nothing alike on site.
In an open attic, installers use loose-fill insulation blown freely between the joists to a target depth.
In an enclosed wall, that same dry fiber gets compacted into a dense-pack, because loose fiber in a vertical cavity would just slump toward the bottom over time.
Loose-fill dry cellulose stays one of the more common attic insulation types for a boring reason. It conforms to whatever joist spacing the original builder felt like using, with no cutting.
- Spray-applied needs a drying period before drywall goes up, which adds a day or two to the schedule
- Stabilized cellulose resists the settling plain loose-fill goes through
Nu-Wool has been manufacturing cellulose since 1949 and sells separate loose-fill and dense-pack lines rated between R-13 and R-60 depending on installed thickness.
How Well Does Cellulose Insulation Insulate?
Installed thermal resistance lands around R-3.2 to R-3.5 per inch, according to the DOE-affiliated Building America Solution Center. Standard loose-fill fiberglass sits below that at equal thickness. Against dense fiberglass batts, the gap mostly closes.
Its R-value comes less from the paper than from how densely the fiber packs into a cavity. Tightly packed fiber traps still air, and still air is what actually resists heat flow.
Because it conforms to irregular framing, it also cuts down on thermal bridging around wiring, pipes, and the odd-shaped joist bays where a rigid batt leaves a visible gap on both sides.
The numbers that come up on an actual job:
- Installed R-value of 3.2 to 3.5 per inch (Building America Solution Center, PNNL)
- R-13 in a standard wall cavity and R-38 in an attic floor as common benchmarks (U.S. Department of Energy and ENERGY STAR climate-zone guidance, citing CIMA and DOE test data)
Settling is the third variable, and it behaves differently by location. Attic loose-fill settles gradually, while dense-packed walls resist settling almost entirely (CIMA technical guidance).
Dense-pack cellulose is the default fill on DOE-funded weatherization work, picked because it holds R-value under compaction better than loose fiberglass does.
Density and settling both feed back into real-world performance. Which is why a good installer weighs the fiber going into a cavity instead of just eyeballing the depth.
Is Cellulose Insulation Safe and Fire Resistant?
Treated paper doesn’t burn the way untreated paper burns. Boric acid and ammonium sulfate shift the behavior from open flame to a slow smolder that self-extinguishes. Nobody’s calling it fireproof, and it isn’t, but it won’t carry flame across an attic.
The borate does double duty. Insects and rodents find the treated fiber unappealing to eat or nest in, and the same chemistry keeps mold from taking hold.
On the compliance side, products meet ASTM C739 for fiber specification, ASTM C1936 for corrosiveness, and the Consumer Product Safety Commission’s flammability rule under 16 CFR Part 1209.
Anything sold in the US also has to carry an insulation fire rating of Class 1 under ASTM E84, the same surface-burning test used across the whole insulation industry.
US GreenFiber’s line, manufactured out of Charlotte, North Carolina, is tested to that Class 1 rating and produces no formaldehyde emissions.
Toxicity, off-gassing, and long-term exposure are their own conversation. A closer look at whether cellulose insulation is actually safe covers those specifics.
How Is Cellulose Insulation Installed?
Whether the cavity is open or already closed up behind finished drywall decides the method entirely.
For an enclosed wall, installers use the dense pack insulation technique, compacting dry fiber through small drilled access holes until the cavity won’t take any more.
- Locate framing and drill access holes near the top of each wall cavity
- Insert the blower hose and pack fiber to the manufacturer’s recommended density
- Move down the cavity in stages so no air pockets form behind the fiber
- Patch and seal each access hole once the cavity reads full pressure
- Check fill consistency with a moisture meter or thermal camera before closing the wall
The blower machine feeds fiber through the hose at controlled, steady pressure. That last verification step gets skipped more often than it should.
Open attic work is much simpler. Loose-fill goes down between the joists to a target depth rather than a target pressure, and depth is something you can check with a ruler.
Settling and Long-Term Coverage
Loose-fill cellulose in an open attic beds down under its own weight and loses some depth over the first year or so.
Dense-packed cellulose in a closed wall doesn’t behave that way. Insulation settlement stops being a real concern once density crosses a threshold.
- Attic loose-fill settles gradually, so installers deliberately over-blow to hit a target settled depth
- Wall dense-pack settling is virtually nil above 3.5 pounds per cubic foot installed density, per CIMA technical guidance
Professional Installation vs DIY
Blowing loose-fill into an open attic is a legitimate weekend job. Rent a blower from a hardware store, watch your depth, wear a respirator, done.
Dense-packing walls is a different animal. The rig has to hold at least 80 inches of water column at the takeoff to pack fiber to the correct density (Building America Solution Center, PNNL), and reading the pressure right takes reps. Get it wrong and you’ve got voids inside a wall you just patched shut.
The Insulation Contractors Association of America certifies installers specifically on dense-pack, which tells you something about which of the two skills is harder to get right.
How Does Cellulose Insulation Compare to Fiberglass and Other Insulation Types?
Among common insulation materials, cellulose sits near the top for recycled content and sound dampening. It is not the leader on raw R-value per inch, and pretending otherwise would be silly.
| Material | R-Value per Inch | Recycled Content | Key Trait |
|---|---|---|---|
| Cellulose | 3.2 to 3.5 | 75 to 85 percent or more | Fills gaps, strong sound dampening |
| Fiberglass batt | 2.9 to 3.8 | 20 to 40 percent | Low cost, easy DIY |
| Mineral wool | 3.3 to 4.0 | Varies by producer | Higher fire and moisture tolerance |
| Spray foam | 3.5 to 6.5 | Low to none | Air seals and insulates in one step |
Those ranges come from published R-value tables from the U.S. Department of Energy and state energy offices, Nebraska’s included, since exact figures shift a little by manufacturer.
Foam is the comparison people actually care about. A full breakdown of spray foam or cellulose insulation walks through the cost and airtightness differences.
Fire is where cellulose and fiberglass diverge most, because cellulose depends on an added borate treatment to get there. Looking at whether fiberglass insulation is flammable shows how untreated glass fiber handles heat with no help.
Cellulose makes sense when you’re dealing with wiring, plumbing runs, and framing that doesn’t match any standard batt width, or when noise between floors is driving you up the wall. Fiberglass wins on price and on how quickly a homeowner can do it themselves.
NAIMA, the trade group for fiberglass and mineral wool producers, publishes its own comparative data as CIMA’s counterpart on the cellulose side. Read both with that in mind.
What Are the Pros and Cons of Cellulose Insulation?
The trade is fairly clean. You get a low-carbon material that fills gaps better than anything short of foam, and in exchange you accept that it handles water worse than most of its competition.
On the plus side:
- High recycled content and a low manufacturing footprint
- Fills irregular framing and wraps around wiring with no cutting
- Strong sound dampening between floors and rooms, which is the reason a lot of people use it in interior walls
- Borate treatment instead of petrochemical additives
The downsides are fewer, and they’re real:
- It absorbs water readily and dries slowly once saturated
- Installation is dusty without proper containment
- It’s heavier than fiberglass, which matters if you’re loading up old ceiling drywall
Builders for Climate Action ran a 2022 BEAM analysis on 11 cavity-fill insulation types, each tested at R-10 across 100 square feet. Dense-packed cellulose ranked lowest for global warming potential. Closed-cell spray foam ranked highest.
That carbon profile is one reason cellulose keeps appearing on lists of the benefits of home insulation that go past plain energy savings.
Its weaknesses trace back to how insulation works at the material level. Anything that traps air to slow heat flow will trap moisture too, if that air ever gets wet.
How Much Does Cellulose Insulation Cost?
Material alone runs about $0.60 to $2.80 per square foot for blown-in cellulose, with the spread depending on loose-fill versus dense-pack (HomeGnome, 2025). Labor usually adds about as much again, since dense-pack work is slower and needs the higher-output blower.
| Job Type | Typical Scope | Main Cost Driver |
|---|---|---|
| Attic loose-fill | Open floor, blown to target depth | Attic size and access |
| Wall dense-pack | Drilled access holes, packed cavity | Wall area and drilling labor |
| Wet-spray | Open studs before drywall goes up | Drying time before close-up |
Federal help changed going into 2026, and not in homeowners’ favor.
The Section 25C insulation tax credit expired for any project placed in service after December 31, 2025, under the One Big Beautiful Bill Act signed in July 2025. Anyone planning a 2026 install is working with state and utility programs instead.
Those still exist and they’re worth chasing. Oncor in Texas pays a per-square-foot weatherization rebate for attics upgraded from R-22 or below to R-38 or better, through its Take a Load Off Texas program.
When Does Cellulose Insulation Not Work Well?
Cellulose doesn’t fail randomly. It fails in a short list of conditions that are known in advance.
Unvented cathedral ceilings are the big one. Building Science Corporation’s Dr. Joseph Lstiburek has said plainly that cellulose only works in that assembly with an adequate layer of rigid foam above the roof sheathing or closed-cell spray foam below it. On its own, it doesn’t belong there.
Below-grade walls are the second. Loose fiber can’t sit directly against concrete or masonry. Anyone insulating basement walls needs a continuous foam or mineral wool layer against the concrete first, because minor seepage is enough to soak cellulose pressed up against that surface, never mind an actual flood.
Then there’s the gap between brick veneer and the block or timber wall behind it. Cellulose is not a recognized fill for that cavity. Rigid board products built for external wall insulation handle that role.
- Sustained plumbing or roof leaks that go unnoticed for days
- Any cavity with no drying path after an occasional wetting event
FAQ on What Is Cellulose Insulation
What Does Cellulose Insulation Look Like?
Loose gray or beige fluff, essentially shredded newspaper pulp with flecks of print and cardboard fiber still visible in it. Once settled it compacts into a denser mat but keeps that fibrous texture, which is what separates it visually from the uniform pink or yellow strands of fiberglass.
Is Cellulose Insulation a Good Choice for Older Homes?
It’s one of the better options, because dense-pack crews drill small holes and fill closed wall cavities without tearing off plaster or siding. That makes it a common pick for retrofit insulation work where open-stud methods like wet-spray simply aren’t available.
How Long Does Cellulose Insulation Last?
Properly installed cellulose insulation lasts as long as the building itself, since the fiber doesn’t decay under normal conditions. It won’t compress or break down the way batt products do. Water damage, pests, or heavy settling can cut that short, though all three are avoidable.
How Do Installers Confirm Cellulose Insulation Was Installed Correctly?
They check installed density against the manufacturer’s coverage chart and probe depth along the cavity. The thorough ones also run a blower door test before and after to measure whole-house air leakage, which confirms the dense-pack actually cut infiltration rather than just adding bulk behind the drywall.
Who Manufactures Cellulose Insulation?
CIMA lists more than a dozen member producers across the U.S. and Canada, among them Greenfiber, Nu-Wool, Applegate, International Cellulose Corporation, and Soprema. Most operate regional plants, because cellulose is light and bulky and shipping it long distances costs more than the product is worth.
How Much Cellulose Insulation Does Your Attic Actually Need?
Cellulose only delivers its rated R-value at the depth your climate zone calls for. A shallow layer under-delivers no matter how well the fiber is packed, and filling the joist bay to the top is not the same thing as hitting the number.
- Measure current depth with a tape or a probe rod
- Compare it against your climate zone’s target R-value
- Add only enough cellulose to close the remaining gap
Topping up costs far less than a full replacement. It also locks in whatever air leaks are already sitting underneath, because new fiber on top does nothing to fix gaps in the layer below.
A closer breakdown of how much insulation your attic actually needs covers target depths by climate zone.
