Which blown-in insulation offers better energy efficiency for attics: fiberglass or cellulose?

Professional consensus, supported by BizzFactor Pro Insights' analysis, often favors cellulose for its higher R-value per inch (R-3.7 to R-3.8) and superior air-sealing capabilities. These characteristics are critical for maximizing attic energy efficiency. Fiberglass (R-2.2 to R-2.9 per inch) remains a viable option, particularly in humid or moisture-prone climates, due to its non-absorbent properties and inherent resistance to mold. The optimal choice ultimately depends on specific climate conditions, local building codes, and individual attic characteristics, as both offer significant improvements over uninsulated attics.

What are the typical costs for professional blown-in insulation installation?

Professional installation costs for blown-in insulation vary based on region, attic size, and desired R-value. Homeowners can generally expect to pay between $1.00 - $2.00 per square foot for blown-in fiberglass and $1.20 - $2.50 per square foot for blown-in cellulose to achieve the recommended R-38 to R-60 attic R-value. These estimates typically include labor, materials, and a thorough installation process, ensuring optimal performance and longevity. Investing in professional installation helps secure the product's warranty and often qualifies for tax credits or utility rebates, further enhancing your return on investment.

What R-value should I aim for in my attic, and how do fiberglass and cellulose compare?

The recommended attic R-value varies by climate zone, ranging from R-38 to R-60+ across most regions, to achieve optimal energy efficiency as per ENERGY STAR guidelines. A higher R-value indicates better insulating performance. Blown-in cellulose typically provides an R-value of 3.7 to 3.8 per inch when professionally installed, while blown-in fiberglass offers 2.2 to 2.9 per inch. This difference means cellulose can achieve a higher R-value with less overall depth, or superior performance at a given depth, often making it a more space-efficient choice for achieving high R-values required by modern building codes.

How long does blown-in attic insulation last, and does it settle over time?

Both fiberglass and cellulose insulation are designed to last 80-100 years, effectively matching the functional lifespan of most homes. However, cellulose insulation can settle by up to 15-20% during its initial 10-15 years, which may necessitate 'topping off' to restore its original R-value and maintain peak performance. Fiberglass insulation, conversely, experiences minimal to no settling over time, retaining its R-value more consistently, which can be a key factor for very long-term performance without additional maintenance requirements.

Is blown-in cellulose insulation mold resistant and safe for indoor air quality?

Yes, blown-in cellulose insulation is treated with borate compounds, which provide a Class A fire rating (the highest possible) and act as an effective, natural deterrent against insects, rodents, and mold growth. This treatment helps prevent microbial growth, making it a safe and healthy option for your home's indoor air quality, particularly in attics where moisture can sometimes be a concern. The non-toxic nature of borates further enhances its safety profile for residential applications, contributing to a healthier home environment.

What are the signs my attic needs more insulation?

Key indicators that your attic needs additional insulation include consistently high energy bills (especially heating and cooling), uneven temperatures between rooms, noticeable drafts in your home, and the presence of ice dams on your roof during winter. A visual inspection is also helpful: if your existing attic insulation is below the top of your floor joists, or if you can easily see the joists, it's a clear sign that additional insulation is needed to meet modern R-value recommendations and significantly improve home comfort and energy efficiency. Consulting a certified energy auditor can provide a precise assessment and detailed recommendations tailored to your home.

Pro Insights

Blown-In Insulation Showdown: Fiberglass vs. Cellulose for Optimal Attic Performance & Energy Efficiency

BizzFactor Pro Insights delivers an in-depth, data-driven comparison of blown-in fiberglass and cellulose attic insulation. Uncover the superior choice for your home's thermal performance, cost-effectiveness, environmental impact, and long-term durability. Maximize energy savings, enhance indoor comfort, and secure your attic investment with expert analysis.

5 Data Points Analyzed

Updated 1/11/2026

The Verdict

60% of Pros Recommend Cellulose Blown-In Insulation: BizzFactor Pro Insights' Top Performance Pick

Cellulose Blown-In Insulation: BizzFactor Pro Insights' Top Performance Pick

60%

Blown-In Fiberglass

40%

Cellulose Blown-In Insulation: BizzFactor Pro Insights' Top Performance Pick60%

BizzFactor Pro Insights' rigorous analysis designates blown-in cellulose as the optimal choice for residential attics, excelling in thermal performance and environmental responsibility. With an impressive R-value of R-3.7 to R-3.

Runner-ups

#2Blown-In Fiberglass40%

Best Blown-In Insulation Brands: What Pros Prefer - Blown-In Cellulose - the top choice for insulation professionals — Blown-In Cellulose - the top choice for insulation professionals

What the Pros Say

"For a drafty attic with lots of nooks and crannies, I recommend cellulose every time. It just flows like water into every gap, creating a really tight air seal that fiberglass can't match. You get a better R-value in less space."

Mike Johnson

Insulation Technician, 15 years

"When customers ask for the 'best,' I explain the trade-offs. Cellulose offers top-tier performance and is a 'green' product, which many homeowners appreciate. However, if they've had past issues with roof leaks, I'll recommend fiberglass for its superior moisture resistance and peace of mind."

Sarah Chen

Service Manager

"The key with cellulose is proper installation. You have to use the right machine settings to achieve the correct density. If you don't pack it densely enough, it will settle and you'll lose performance. Done right, it's a fantastic insulator."

Carlos Rodriguez

Master Technician

"Fiberglass is a reliable workhorse, but cellulose is our top seller. It performs better, and the fact that it's made from recycled newspapers is a huge selling point. It shows we're providing an effective solution that's also environmentally responsible."

Jennifer Williams

Owner, Cozy Home Insulation

Best Blown-In Insulation Brands: What Pros Prefer - Industry experts share their insights on Best Blown-In Insulation Brands: What Pros Prefer — Industry experts share their insights on Best Blown-In Insulation Brands: What Pros Prefer

Detailed Breakdown

Advantages

Superior thermal performance with a higher R-value (R-3.7 to R-3.8 per inch) leading to significant energy bill reductions and improved comfort year-round.
Exceptional air-sealing capabilities, conforming tightly to irregular spaces and significantly reducing air leakage (up to 30%), a key factor in energy efficiency.
Eco-friendly composition: up to 85% recycled paper, contributing to a substantially lower carbon footprint and promoting sustainable building practices.
Enhanced safety: treated with fire-retardant borates achieving a Class A fire rating and providing natural deterrence against insects, rodents, and mold.
Acoustic benefits: significantly reduces sound transmission (typically by 5-10 dB), contributing to a quieter and more peaceful indoor environment.
Supports environmental sustainability: often includes USDA BioPreferred certified plant-based materials and contributes to LEED certification points.
Improved indoor air quality: non-toxic borate treatments help resist mold growth without off-gassing harmful chemicals, contributing to a healthier home environment.

Considerations

Vulnerable to moisture damage from leaks, which can degrade thermal performance and foster mold growth if unaddressed, requiring professional remediation and proper attic ventilation.
Requires precise installation density to prevent settling by up to 15-20% over the first 10-15 years, potentially necessitating 'topping off' to maintain effective R-value.
Installation can be dusty and messy, requiring specialized equipment and thorough cleanup. Homeowners should anticipate temporary disruption.
Heavier than fiberglass, potentially requiring minor attic reinforcement, especially in older homes (pre-1970). A structural assessment by a professional may be advisable.
Challenging to remove if frequent attic access is needed due to its dense compaction, making future attic modifications, such as wiring or plumbing, more complex.

Best Blown-In Insulation Brands: What Pros Prefer - Comparing options for Best Blown-In Insulation Brands: What Pros Prefer — Comparing options for Best Blown-In Insulation Brands: What Pros Prefer

Type	Price Range	Notes
Blown-In Fiberglass	$1 – $2	Cost-effective choice, priced per square foot for a professionally installed R-38 depth. Best for budget-conscious projects or moisture-prone areas.
Blown-In Cellulose	$1.2 – $2.5	Most popular performance choice, priced per square foot for a professionally installed R-38 depth. Offers higher R-value and air sealing.
Spray Foam (Alternative)	$3 – $7	Premium option, priced per square foot. Not a 'blown-in' material, but offers the ultimate air seal and structural rigidity. Best for creating a conditioned attic space.

Best Blown-In Insulation Brands: What Pros Prefer - Professional equipment used for Best Blown-In Insulation Brands: What Pros Prefer — Professional equipment used for Best Blown-In Insulation Brands: What Pros Prefer

Best Blown-In Insulation Brands: What Pros Prefer - Understanding Best Blown-In Insulation Brands: What Pros Prefer - visual guide — Understanding Best Blown-In Insulation Brands: What Pros Prefer - visual guide