Cellulose Insulation: R-Value, Cost, Pros & Cons Guide (2026)

Quick Answer: Cellulose insulation is made mostly from recycled newspaper treated with borate fire retardants. It delivers R-3.2 to R-3.8 per inch ^[1][2][3] at $0.60–$2.30/sq ft installed (loose-fill) or $1.50–$3.00/sq ft (dense-pack walls), making it one of the best values in insulation. Loose-fill is blown into open attics; dense-pack is blown under pressure into enclosed wall cavities. The main drawback is that loose-fill settles about 10% over the first year or two, so manufacturers' coverage charts already build in the extra installed depth needed to reach the labeled R-value.

Table of Contents

• What Is Cellulose Insulation?
• Loose-Fill vs Dense-Pack Cellulose
• R-Value Performance
• The Settling Reality
• Air Sealing Properties
• Fire Safety
• Moisture Behavior
• DIY Installation (Attic Loose-Fill)
• Dense-Pack Wall Retrofit
• Cost Analysis
• Environmental Credentials
• When Cellulose Beats Fiberglass
• Common Mistakes
• Key Takeaways
• FAQ

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What Is Cellulose Insulation?

Cellulose insulation is recycled newspaper ground into dense fibers and treated with borate-based fire retardants. The borates serve triple duty: fire retardant, mold inhibitor, and pest deterrent. It's manufactured as dry, loose fibers and installed with a blowing machine, either as low-density loose-fill in open attic spaces or as high-density dense-pack in enclosed wall cavities.

Shredded newspaper is inherently a good insulator because of the millions of tiny air pockets trapped between fibers. The borate treatment is what makes it building-code compliant and long-lasting. Without the treatment, you'd essentially be blowing flammable newspaper into your walls, and the borates are what separate building insulation from a fire hazard.

Cellulose has a long track record in US homes and is manufactured by dozens of companies. Major brands include GreenFiber (the largest US manufacturer), Nu-Wool, Applegate, and National Fiber. The products are largely commodity — unlike fiberglass or mineral wool where brand differentiation is meaningful, most cellulose products perform comparably.

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Loose-Fill vs Dense-Pack Cellulose

These are the same base material installed at very different densities for very different applications. They're not interchangeable.

Sources: manufacturer density and per-inch data ^[2][4][5][6]; settling built into coverage charts ^[1][7].

Loose-fill is the product you'll encounter at Home Depot and Lowe's — bags of fluffy cellulose blown through a hose onto your attic floor. It's a commodity product with a commodity price. At 1.5 lb/ft³, it's light enough to pile to any depth on an attic floor but settles significantly over time.

Dense-pack is the same material blown under much higher pressure into enclosed cavities — typically through 2–3 inch holes drilled in exterior siding or interior drywall. At 3.0–3.5 lb/ft³, it's packed tightly enough to resist settling and provides meaningful air-sealing properties that loose-fill doesn't. Dense-pack is the gold standard for retrofitting existing walls without removing drywall.

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R-Value Performance

Cellulose delivers R-3.2 to R-3.8 per inch at settled thickness, depending on density and installation ^[1][3] — competitive with standard fiberglass batts (R-3.0–R-3.7) ^[8][9] and open-cell spray foam (R-3.5–R-3.8). It's lower than mineral wool (R-3.8–R-4.3) and significantly lower than closed-cell spray foam (R-6.0–R-7.0) ^[10][11]. Per-inch R-values vary with installed thickness. For the full ranking, see our R-value per inch chart.

Attic Depth Chart (Settled Thickness)

This is the chart you need when specifying an attic cellulose job. All depths reflect settled thickness — the insulation will be installed deeper and settle to these values.

Sources: settled depths and bag coverage from manufacturer charts ^[1][4][2][7].

At R-49, you're looking at approximately 14 inches of settled cellulose. Installed depth should be about 14.5–16.1 inches, roughly 11% above the settled target for dry loose-fill, which the coverage chart already accounts for. Bag counts vary by manufacturer — always check the coverage chart printed on the bags.

For a cross-material thickness comparison, see our insulation thickness chart and R-value insulation chart.

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The Settling Reality

This is cellulose's most discussed limitation. Loose-fill cellulose settles about 10% in the first year or two after installation (Applegate and Nu-Wool charts build in about 10%; Cel-Pak 9.6–11.6%). ORNL (1992) measured a 9% thickness loss and a 6–10% R-value loss ^{[1][4][2][12]}. This is not a defect; it's an inherent property of a low-density fibrous material under gravity.

What settling means in practice: labeled R-values are rated at settled density (FTC 16 CFR 460.5) ^[3], so an attic filled to the chart's initial installed depth does not fall below its target R-value as it settles. Fourteen inches of dry loose-fill settles about 10% to roughly 12.6 inches, close to R-42, not down to 11 inches or R-38.

How to compensate: Reputable installers account for settling by over-filling. The coverage charts on cellulose bags specify bags-per-1,000-sq-ft at the settled density, so if your installer follows the manufacturer's chart, the settling is already accounted for. The problem occurs when installers eyeball the depth instead of counting bags and measuring installed thickness.

Dense-pack cellulose settles much less. At 3.0–3.5 lb/ft³ density in enclosed wall cavities, there's very little room for the material to compress further ^[6][2]. Settling in dense-pack walls is minimal, comparable to blown-in fiberglass (about 1% or less) ^[13][14].

Settling should not stop you from choosing cellulose. It is a known quantity that's fully manageable by installing to the correct initial depth, and every cellulose manufacturer accounts for it in their coverage charts. Cellulose remains a well-established attic insulation. Just make sure the installer fills to the chart's initial installed depth, then use a ruler or measuring stick to check depth in at least 6–8 locations across the attic before they leave. Installed depth should be about 11% above your target settled depth for dry loose-fill ^[2][15]; for an R-49 target (14" settled), that means about 14.5–16.1 inches. Take photos with the ruler for your records, which help if you ever need to verify performance or file a warranty claim.

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Air Sealing Properties

Dense-pack cellulose provides significantly better air sealing than fiberglass batts — though it's not a true air barrier like spray foam.

Dense-pack cellulose installed at proper density (3.0–3.5 lb/ft³) ^[6][2] resists airflow through wall assemblies better than fiberglass batts. The mechanism is straightforward: at 3.5 lb/ft³, cellulose fibers are packed tightly enough that air has difficulty moving through the material. It's not an air barrier by code definition, but the practical air-sealing performance is meaningful.

Loose-fill cellulose in attics provides minimal air sealing at its lower density (1.5 lb/ft³). You should still air seal your attic floor before blowing cellulose — seal penetrations, top plates, recessed lights, duct boots, and chimney chases first, then insulate over the sealed surface. ENERGY STAR estimates that air sealing plus insulation together save a household an average of 15% of heating and cooling costs (about 11% of total energy use), with 7–20% of heating and cooling costs depending on climate zone ^[16][17].

For wall retrofits, this air-sealing behavior is one of dense-pack cellulose's advantages over fiberglass. In a drill-and-fill of an existing wall cavity, there's no interior access to caulk and foam-seal individual penetrations. Dense-pack cellulose provides a measure of air sealing as it fills, partially compensating for the inability to perform traditional air sealing in enclosed cavities.

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Fire Safety

Cellulose's fire story is nuanced and frequently misunderstood.

The material itself is combustible. It's recycled newspaper. The borate fire retardant treatment is what makes it code-compliant. Manufacturers report that treated cellulose carries a Class A fire rating under ASTM E84. Class A, as defined by the International Building Code (IBC 2021 §803.1.2, tested to ASTM E84), means a flame-spread index of 0–25 and a smoke-developed index of 0–450 ^[18].

Cellulose sits at the higher-smoke end of Class A. Its smoke-developed index is well above mineral wool (SDI 0) and unfaced fiberglass, which meets flame-spread ≤25 and smoke-developed ≤50 under the ASTM C665 product standard for unfaced blankets ^[19][20]. The ≤50 figure is a product-standard limit, not the Class A threshold. In a fire, cellulose will produce more smoke than mineral wool or fiberglass.

Cellulose chars rather than flames. When exposed to fire, properly treated cellulose forms a char layer that resists further combustion. It smolders rather than producing open flame. This is a genuine fire-safety advantage over untreated materials, but it's fundamentally different from mineral wool, which simply doesn't burn.

The borate treatment is permanent under normal conditions. It doesn't wash out or degrade inside dry wall cavities. The concern is prolonged moisture exposure — if cellulose gets and stays wet, the borates can leach out over time, reducing fire resistance. This is another reason to keep cellulose dry.

For more on fire-rated materials, see our mineral wool insulation guide.

Pro Tip: If fire resistance is your primary concern, say you're in a wildfire zone, insulating a garage-to-house wall, or building a fire-rated assembly, mineral wool is the clear choice at FSI 0, SDI 0, and noncombustible (ASTM E136). Cellulose's Class A rating is adequate for general residential use, but mineral wool is far ahead for fire safety.

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Moisture Behavior

Cellulose is hygroscopic — it absorbs and releases moisture depending on the surrounding humidity. This is both a feature and a risk.

The advantage: In wall assemblies with variable humidity, cellulose acts as a moisture buffer. It absorbs excess moisture during humid periods and releases it when humidity drops. This buffering capacity can help a wall assembly manage transient moisture loads better than non-hygroscopic materials like fiberglass.

The risk: Prolonged moisture exposure causes cellulose to clump, sag, and lose R-value. If a wall leak saturates the cellulose, drying can take weeks — and during that time, the wet cellulose can promote mold growth on adjacent wood framing and sheathing. The borate treatment resists mold growth on the cellulose itself, but wet cellulose against wet wood is a recipe for problems.

Vapor permeability is moderate, allowing some drying through the material but not as freely as mineral wool or unfaced fiberglass, which are more open to vapor.

Bottom line: Cellulose is appropriate for standard wall and attic applications with proper moisture management. It should NOT be used in perpetually wet locations (crawl spaces, below-grade, exterior exposure). For moisture-prone applications, use closed-cell spray foam or mineral wool. For moisture management principles, see our crawl space vapor barrier guide.

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DIY Installation (Attic Loose-Fill)

Blowing loose-fill cellulose into an open attic is one of the most accessible and cost-effective DIY insulation projects. For many homeowners it's the single biggest energy improvement available with a fast payback.

Equipment: A blowing machine is required. Home Depot and Lowe's offer free machine rental with purchase of 20+ bags of cellulose (approximately $12–$15 per bag). Twenty bags cover about 280–360 sq ft at R-49 ^[1][4]. Third-party machine rental runs approximately $100/day.

Basic process:

1. Air seal the attic floor first — seal all penetrations, top plates, duct boots, and recessed lights with caulk and canned foam
2. Install baffles at each rafter bay near the eaves to maintain soffit ventilation clearance
3. Set up the blowing machine at the attic access (or below, running the hose up)
4. Blow cellulose to the target depth — check the bag's coverage chart for bags-per-1,000-sq-ft
5. Install depth markers (rulers or pre-cut sticks) across the attic to verify consistent depth
6. Verify installed depth is about 11% above target settled depth

Safety gear: N95 respirator (mandatory — cellulose dust is a lung irritant), safety glasses, headlamp, long sleeves, gloves. Kneeling boards to distribute weight on ceiling joists (never step between joists on drywall).

What it costs DIY: Material for 1,000 sq ft at R-49: roughly 56–71 bags at $12–$15/bag = $360–$540 in material with a free machine. Compare to $1,200–$3,500 professionally installed. That's a 60–80% savings. For detailed step-by-step instructions, see our guide on how to install blown-in insulation.

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Dense-Pack Wall Retrofit

Dense-pack cellulose is the #1 method for insulating existing wall cavities without demolishing drywall or removing siding.

The process:

1. Drill 2–3 inch holes through exterior siding (preferred) or interior drywall — one hole per stud bay, typically at the top of the wall
2. Insert a fill tube through the hole down to the bottom of the cavity
3. Blow cellulose under high pressure, slowly withdrawing the tube as the cavity fills from bottom to top
4. Target density: 3.0–3.5 lb/ft³ — firm enough that you can't push a finger into the material
5. Plug holes with wood or foam plugs, patch, caulk, and repaint

This is a professional job. Dense-pack requires a commercial blowing machine with higher pressure than consumer rental machines, a fill tube technique that takes practice, and the ability to judge density by feel and sound. Under-packed cavities (below 3.0 lb/ft³) will settle and leave gaps. Over-packed cavities can bow drywall or push out siding.

What you get: A 2×4 wall filled with dense-pack cellulose delivers approximately R-13 (3.5" × R-3.7/inch). A 2×6 wall delivers R-20 to R-21 ^[2][4][5]. Plus a meaningful air-sealing improvement over an empty cavity.

Cost for dense-pack wall retrofit: $1.50–$3.00/sq ft installed. A 1,500 sq ft home with approximately 1,000 sq ft of exterior wall area runs $1,500–$3,000. See our guide on insulating walls without removing drywall.

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Cost Analysis

Cellulose is one of the most cost-effective insulation materials, especially for attic applications.

Cost Per R-Value Comparison

For a 1,000 sq ft attic blown to R-49: cellulose costs $600–$2,300 installed (or $300–$500 DIY). As a package, air sealing plus insulation in a typical 1970–1989 home saves an average of 15% of heating and cooling costs (7–20% depending on climate zone), per ENERGY STAR ^[16][17]. An attic upgrade from R-19 to R-49 saves $200–$400 per year in heating and cooling costs for a 1,500 sq ft home, putting the payback period at 1–5 years depending on your starting condition and climate zone.

For personalized project pricing, use our insulation cost calculator or see blown-in insulation cost for detailed breakdowns.

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Environmental Credentials

Cellulose has the strongest environmental profile of any common insulation material — and it's not close.

High recycled content. Cellulose is made largely from recycled newspaper, diverting paper from the waste stream. Its recycled content is higher than that of fiberglass (recycled glass), mineral wool (recycled slag), or spray foam.

Low embodied energy. Grinding newspaper and adding borate is far less energy-intensive than melting glass or rock at thousands of degrees.

Borate fire retardant is a naturally occurring mineral. Borax and boric acid are mined compounds. They don't off-gas, don't break down under normal conditions, and are used widely in residential applications.

End-of-life: Cellulose can be removed and recycled or composted. It's biodegradable. This is a meaningful advantage over spray foam (goes to landfill, cannot be recycled) and rigid foam boards (some recyclable, most go to landfill).

If environmental impact is a priority for your project, cellulose is a strong choice. The federal 25C tax credit for insulation is described by the IRS and ENERGY STAR ^[21][22], and DOE Home Energy Rebates are now available in select states and cover insulation and air sealing ^[23]. Utility and state programs vary, so check what applies locally.

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When Cellulose Beats Fiberglass

Attic blow-in: Cellulose flows around obstructions (wiring, plumbing, junction boxes) better than fiberglass batts. No gaps, no voids, no compression around irregular shapes. Blown-in cellulose in an attic typically delivers closer to its rated R-value than batts because the coverage is more uniform.

Wall retrofits: Dense-pack cellulose is the only practical option for insulating existing walls via drill-and-fill. Blown-in fiberglass doesn't achieve the same density, and batts require cavity access. See insulate walls without removing drywall.

Air sealing (dense-pack): Dense-pack cellulose at 3.0–3.5 lb/ft³ ^[6] resists airflow through a wall assembly better than fiberglass batts. For retrofit wall applications where traditional air sealing isn't possible, this passive air sealing is a significant advantage.

Environmental priority: Higher recycled content than fiberglass. Lower manufacturing energy. Compostable end-of-life.

When Fiberglass Wins

Wet-prone areas: Fiberglass doesn't absorb water chemically (though it traps it). Cellulose is hygroscopic and degrades with prolonged moisture. Neither is ideal for wet locations, where closed-cell spray foam or mineral wool are better, but fiberglass recovers more predictably from occasional wetting.

Long-term stability: Blown-in fiberglass settles about 1% or less ^[13][24] versus cellulose's roughly 10%. In an attic where you want install-and-forget performance, fiberglass holds its depth better over decades.

Non-combustibility: Unfaced fiberglass meets flame-spread ≤25 and smoke-developed ≤50 and is noncombustible (ASTM E136) ^[19]. Cellulose is treated-combustible and carries a Class A rating, but sits at the higher-smoke end of that class. For applications where fire is a primary concern, fiberglass is better and mineral wool is best.

New construction walls: With open cavities and a competent installer, fiberglass batts deliver comparable R-value to cellulose at lower cost. Dense-pack cellulose in new construction is possible but less common.

For the full comparison, see fiberglass vs. cellulose.

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Common Mistakes

1. Not accounting for settling in attic installations. Installing to the exact settled R-value depth leaves you about 10% under target once dry loose-fill settles. Install to about 11% above the settled depth specification. If the bag chart lists a 14-inch settled depth for R-49, install to about 14.5–16.1 inches ^[2][15].

2. Using cellulose in perpetually wet locations. Cellulose absorbs moisture and degrades over time in wet conditions. Crawl spaces, basement walls, and any below-grade application should use closed-cell spray foam or rigid foam — not cellulose.

3. Attempting dense-pack as a DIY project. Dense-pack cellulose requires commercial-grade blowing equipment, proper fill tube technique, and the ability to judge density by sound and feel. Consumer rental machines don't generate enough pressure. Under-packed walls settle and leave voids; over-packed walls bow drywall. This is a professional skill.

4. Skipping air sealing before blowing the attic. Loose-fill cellulose at 1.5 lb/ft³ does NOT air seal. If you blow cellulose over unsealed attic floor penetrations, top plates, and recessed lights, warm air still leaks through those gaps — carrying moisture into the cold attic and reducing the effective R-value. Air seal first, insulate second. See our guide on how to air seal an attic.

5. Overloading old ceilings. Cellulose at R-49 (14 inches settled) weighs approximately 1.5 lbs/ft³ × 14 inches = roughly 1.75 lbs per square foot across the attic ^[25][2]. On older homes with ½-inch drywall and 24-inch on-center framing, verify the ceiling can support the load. Most modern ceilings handle it fine, but pre-1960s homes with plaster or thin drywall may need reinforcement. If the existing ceiling is sagging or cracked, address that before adding weight.

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For a detailed material matchup, read fiberglass vs. mineral wool.

Key Takeaways

• Two forms: loose-fill (1.5 lb/ft³, for open attics, DIY-feasible) and dense-pack (3.0–3.5 lb/ft³, for wall retrofits, professional only).
• Loose-fill settles about 10% in the first year or two. Install about 11% above target depth to compensate. Manufacturers account for this in their bag coverage charts.
• Dense-pack cellulose provides meaningful air sealing and is a leading choice for insulating existing walls without removing drywall.
• Made largely from recycled newspaper, with high recycled content. Low embodied energy and compostable at end of life.
• Class A fire rated thanks to borate treatment, but technically combustible — mineral wool is superior for fire-critical applications.
• Hygroscopic — absorbs and releases moisture. Appropriate for standard walls and attics but not for wet or below-grade locations.
• DIY attic blown-in cellulose is one of the most cost-effective home energy improvements: $300–$500 in material for 1,000 sq ft at R-49, with a 1–5 year payback.
• Dense-pack wall retrofit: $1.50–$3.00/sq ft installed — hire a professional for proper density and coverage.

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FAQ

How long does cellulose insulation last?

Kept dry and undamaged, cellulose can last for the life of the building. In practice its performance depends on moisture control, settling, and freedom from pest disturbance. Loose-fill settles about 10% early on and is rated at its settled density, so an attic filled to the chart's installed depth holds its target R-value. Dense-pack cellulose in walls holds performance well because its higher density resists settling. In attics, check depth every few years and top up if it has settled below your target.

Is cellulose insulation safe?

Yes. Cellulose insulation is considered safe for residential use. Its borate fire retardants are the same family of compounds used in household products. The cellulose fibers can cause respiratory irritation during installation (wear an N95 respirator and safety glasses), but once installed behind drywall or in an attic, there's no ongoing exposure concern. There are no known carcinogenic risks.

Can I blow cellulose on top of existing fiberglass?

Yes, and this is one of the most common and effective insulation upgrades. R-values of continuous layers add: if you have R-19 of existing fiberglass and blow R-30 of cellulose on top, you get approximately R-49 total ^[26][27]. A few important steps: remove or slash any existing vapor retarder (kraft facing) on the old fiberglass to prevent moisture trapping between layers, verify the existing insulation is dry and free of mold or pest damage, and air seal the attic floor before adding new material. See our R-value chart for target R-values by climate zone.

Is cellulose or fiberglass better for attic insulation?

Both work well. Cellulose provides better coverage around obstructions and offers modest air-sealing properties at higher densities. Fiberglass (blown-in) settles significantly less (about 1% or less vs roughly 10% for cellulose). Cellulose has higher recycled content. Fiberglass is noncombustible; cellulose is treated-combustible. For most attics the choice is close: cellulose has an edge in conformity and coverage, while blown-in fiberglass is a solid choice if minimal settling matters most. See fiberglass vs. cellulose for the full comparison.

What R-value does cellulose insulation have?

Cellulose delivers R-3.2 to R-3.8 per inch at settled thickness, depending on density ^[1][6][28]. Loose-fill (attic application) at settled density provides roughly R-3.2–R-3.5 per inch. Dense-pack (wall application) at 3.0–3.5 lb/ft³ delivers R-3.6–R-3.8 per inch. To hit common targets: R-30 requires about 8.5–9 inches settled depth, R-38 needs 10.5–11 inches, R-49 needs 13.5–14.5 inches, and R-60 needs 16.5–17.5 inches ^[4][2]. See the depth chart above and our R-value insulation chart for cross-material comparisons.