Cellulose Insulation: R-Value, Cost, Pros & Cons — Complete Guide

Quick Answer: Cellulose insulation is made from approximately 80% recycled newspaper treated with borate fire retardants. It delivers R-3.2 to R-3.8 per inch 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: loose-fill settles approximately 20% over the first few years, so you need to install extra depth to hit your target 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

---

What Is Cellulose Insulation?

Cellulose insulation is 80–85% recycled newspaper ground into dense fibers and treated with borate-based fire retardants (typically boric acid and ammonium sulfate). 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.

The concept is straightforward: 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 — the borates are what separate building insulation from a fire hazard.

Cellulose has been used in US homes since the 1970s 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.

---

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.

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.

---

R-Value Performance

Cellulose delivers R-3.2 to R-3.8 per inch depending on density and installation — competitive with standard fiberglass batts (R-3.0–R-3.7) 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). 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.

At R-49, you're looking at approximately 14 inches of settled cellulose. Installed depth should be 17–18 inches to account for the ~20% settling that occurs in the first few years. 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.

---

The Settling Reality

This is cellulose's most discussed limitation, and we think the industry undersells it. Loose-fill cellulose settles approximately 20% in the first few years after installation. This is not a defect — it's an inherent property of a low-density fibrous material under gravity.

What settling means in practice: if you install 17.5 inches of loose-fill cellulose in your attic today, it will compress to roughly 14 inches over the first 2–3 years. If you install to exactly the settled R-49 depth (14 inches) without accounting for settling, you'll end up with about 11 inches — roughly 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. Settling in dense-pack walls is typically 2–5% — comparable to blown-in fiberglass (1–3%).

Should settling stop you from choosing cellulose? No. Settling is a known quantity that's fully manageable by installing to the correct initial depth. Every cellulose manufacturer accounts for it in their product specifications. The DOE's insulation guidance still recommends cellulose as a top-performing attic insulation. Just make sure your installer over-fills per the bag chart, and verify depth with a ruler before they leave.

Pro Tip: After your cellulose installation, use a ruler or measuring stick to check depth in at least 6–8 locations across the attic. Depth should be 20–25% above your target settled depth. If your target is R-49 (14" settled), installed depth should be 17–18 inches. Take photos with the ruler for your records — useful if you ever need to verify performance or file a warranty claim.

---

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.

Building Science Corporation research has shown that dense-pack cellulose installed at proper density (3.0–3.5 lb/ft³) reduces air leakage through wall assemblies by 30–40% compared to 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. The DOE estimates that proper air sealing alone saves 10–20% on heating and cooling costs.

This air-sealing advantage is one of the main reasons we recommend dense-pack cellulose over fiberglass for wall retrofits. When you drill-and-fill an existing wall cavity, you can't access the interior 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.

---

Fire Safety

Cellulose's fire story is nuanced and frequently misunderstood.

The material itself is combustible. It's recycled newspaper. Untreated newspaper ignites at approximately 400°F. The borate fire retardant treatment is what makes it code-compliant — treated cellulose achieves a Class A fire rating with a Flame Spread Index of ≤25.

The Smoke Development Index is ≤450 — much higher than mineral wool (SDI 0) and unfaced fiberglass (SDI ≤50). In a fire, cellulose will produce significantly 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 the full fire rating comparison across all materials, see our insulation fire safety guide.

Pro Tip: If fire resistance is your primary concern — 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, non-combustible to 2,150°F. Cellulose's Class A rating is adequate for general residential use, but mineral wool is in a different league for fire safety.

---

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. Building science research suggests this buffering capacity can help wall assemblies 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 approximately 4–6 perms — moderately vapor-permeable, allowing some drying through the material but not as freely as mineral wool (~30+ perms) or fiberglass (~30+ perms unfaced).

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 vapor barrier guide.

---

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. It's the project we recommend to homeowners who want to make the single biggest energy improvement to their home with the fastest 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). That's usually enough for 500–700 sq ft of R-49 coverage. 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 20–25% 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 30–36 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.

---

Dense-Pack Wall Retrofit

Dense-pack cellulose is the #1 method for insulating existing wall cavities without demolishing drywall or removing siding. We've done hundreds of these jobs, from 1890s Victorians to 1970s ranches.

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-19 to R-21. Plus meaningful air-sealing improvement — typically a 20–30% reduction in wall air leakage versus empty cavities.

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.

---

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). The DOE estimates that 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.

---

Environmental Credentials

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

80–85% recycled content — the highest of any insulation. Every bag diverts roughly 40 newspapers from the waste stream. Compare to fiberglass (40–60% recycled glass), mineral wool (~37% recycled slag), and spray foam (0% recycled content).

Low embodied energy — manufacturing cellulose requires approximately 1/10th the energy of fiberglass production. 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 with low toxicity. They don't off-gas, don't break down under normal conditions, and are safe 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 the clear winner. Pair it with Energy Star's guidance on insulation upgrades and available tax credits and rebates for even better ROI.

---

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 reduces air leakage by 30–40% compared to fiberglass batts. For retrofit wall applications where traditional air sealing isn't possible, this passive air sealing is a significant advantage.

Environmental priority: 80–85% recycled content versus 40–60% for 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 — closed-cell spray foam or mineral wool are better — but fiberglass recovers more predictably from occasional wetting.

Long-term stability: Blown-in fiberglass settles only 1–3% versus cellulose's ~20%. In an attic where you want install-and-forget performance, fiberglass holds its depth better over decades.

Non-combustibility: Unfaced fiberglass is non-combustible (FSI ≤25, SDI ≤50). Cellulose is treated-combustible (FSI ≤25 but SDI ≤450). 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.

---

Common Mistakes

1. Not accounting for settling in attic installations. Installing to the exact settled R-value depth guarantees you'll end up 20% under target. Install to 20–25% above the settled depth specification. If the bag chart says 14 inches for R-49, install to 17–18 inches.

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 air sealing vs. insulation.

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. 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.

---

For detailed material matchups, read cellulose vs mineral wool and spray foam vs cellulose.

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 approximately 20% in the first few years. Install 20–25% above target depth to compensate. Manufacturers account for this in their bag coverage charts.
• Dense-pack cellulose provides significant air sealing (30–40% reduction in air leakage vs fiberglass batts) and is the #1 choice for insulating existing walls without removing drywall.
• Made from 80–85% recycled newspaper — the highest recycled content of any insulation. Low embodied energy and compostable at end of life.
• Class A fire rated (FSI ≤25) 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.

---

FAQ

How long does cellulose insulation last?

The cellulose material can last 80+ years if it stays dry and undamaged. However, the effective performance lifespan is closer to 20–30 years because of settling (loose-fill loses ~20% of depth), potential moisture issues in improperly managed assemblies, and the possibility of pest disturbance. Dense-pack cellulose in walls tends to last longer at full performance because its higher density resists settling. In attics, plan on checking depth every 5–10 years and topping up if settled below your target. For comparison, mineral wool maintains performance for 50+ years with virtually no degradation, and spray foam lasts 80+ years.

Is cellulose insulation safe?

Yes. Cellulose insulation is considered safe for residential use. The borate fire retardants (boric acid and ammonium sulfate) have low mammalian toxicity — they're the same compounds used in household pest control 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. For the detailed safety analysis, see Is Cellulose Insulation Safe?.

Can I blow cellulose on top of existing fiberglass?

Yes — and this is one of the most common and effective insulation upgrades. R-values are additive: if you have R-19 of existing fiberglass and blow R-30 of cellulose on top, you get approximately R-49 total. 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 (1–3% vs 20%). Cellulose has higher recycled content (80% vs 40–60%). Fiberglass is non-combustible; cellulose is treated-combustible. On balance, we give a slight edge to cellulose for most attic applications because of its superior conformity and coverage — but blown-in fiberglass is a perfectly solid choice, especially if you prefer minimal settling. 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 depending on density. 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-3.5–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. See the depth chart above and our R-value insulation chart for cross-material comparisons.