Closed Cell Spray Foam vs Blown-In Insulation (Fiberglass & Cellulose)

Choosing the right insulation can be challenging, especially when deciding between spray foam vs blown-in insulation methods. While both provide thermal protection, they differ significantly in R-value, air sealing, and moisture resistance. 

Whether comparing foam insulation vs blown-in for a new project or debating between blown insulation cellulose vs fiberglass, understanding their strengths and weaknesses will help you make the best decision. 

This guide will walk you through the pros, cons, and ideal use cases for each insulation type, ensuring you choose the right solution for your home.

What Is Closed-Cell Spray Foam Insulation?

Closed-cell spray foam insulation is a high-performance solution that combines insulation and air sealing in a single application. Unlike traditional materials, this polyurethane-based foam expands upon application, filling gaps, cracks, and irregular spaces to create a seamless, airtight barrier.

The U.S. Department of Energy highlights that closed-cell spray foam has an industry-leading R-value of 6.0 to 7.0 per inch, making it one of the most thermally efficient insulation options available. Its dense structure not only prevents heat loss but also acts as a moisture barrier, preventing water infiltration and reducing the risk of mold growth.

Additionally, its rigidity enhances structural strength, making it an excellent choice for the insulation of crawl space areas, basements, and walls where durability is crucial. Unlike blown-in insulation, closed-cell spray foam does not settle over time, ensuring long-term energy efficiency.

What Is Blown-In Insulation?

Blown-in insulation refers to a loose-fill material—typically fiberglass or cellulose—that is blown into attics, wall cavities, and other spaces using specialized equipment. When insulating existing walls, small holes must be drilled into the drywall or exterior siding to inject the insulation, and these holes must be patched afterward. DIY installation requires renting a blowing machine, and improper application can leave gaps, reducing efficiency. Its primary advantage lies in its ability to cover large areas quickly and conform around obstacles like wiring and plumbing, making it an effective solution for retrofitting existing homes.

However, unlike expanding foam insulation, blown-in insulation does not create a continuous air seal. It relies on layering and density to provide thermal resistance, which can be compromised over time as the material settles.

In the blown-in insulation vs spray foam debate, blown-in options are generally more affordable upfront but may not offer the same long-term benefits. Fiberglass and cellulose can absorb moisture, reducing their insulating ability, whereas closed-cell spray foam maintains its efficiency even in damp conditions.

What Are the Types of Blown-In Insulation?

There are two primary types of blown-in insulation: fiberglass and cellulose. Each has distinct characteristics that impact its performance, durability, and cost-effectiveness.

• Fiberglass Blown-In Insulation: Made from tiny glass fibers, blown-in fiberglass insulation is lightweight and non-combustible. It provides moderate thermal resistance but is less effective at air sealing compared to spray foam. Additionally, fiberglass can lose R-value if it absorbs moisture, reducing its efficiency over time.
• Cellulose Blown In Insulation: Primarily composed of recycled paper products treated with fire retardants, blown-in cellulose insulation is denser than fiberglass, offering better thermal performance per inch. However, it is more susceptible to moisture damage, which can lead to mold growth and reduced insulating capacity.

In the fiberglass vs cellulose blown insulation debate, cellulose has a higher R-value but requires better moisture control, whereas fiberglass resists moisture absorption but provides lower thermal efficiency. Compared to spray foam insulation, both materials lack air-sealing capabilities, with fiberglass offering lower R-value and cellulose being more vulnerable to moisture. If air sealing and durability are priorities, cellulose vs spray foam or fiberglass vs spray foam comparisons favor closed-cell spray foam.

How Does Closed-Cell Spray Foam Compare to Blown-In Insulation?

Choosing between spray foam vs blown-in insulation depends on factors such as energy efficiency, air sealing, moisture resistance, and longevity. The table below outlines the key differences:

Feature	Closed-Cell Spray Foam	Blown-In Fiberglass	Blown-In Cellulose
R-Value (Thermal Efficiency)	5.6-8.0 per inch	2.2-2.7 per inch	3.5-3.8 per inch
Air Sealing	Creates a seamless, airtight barrier	Poor to Fair	Fair
Moisture Resistance	Acts as a vapor barrier, preventing water infiltration	Absorbs moisture, reducing effectiveness	Treated for moisture resistance but still vulnerable
Mold & Pest Resistance	No organic material for mold or pests	Non-organic, resists mold	Borate-treated for pest resistance but can develop mold when wet
Soundproofing	Moderate noise reduction	Limited sound dampening	Good sound absorption
Durability	Rigid, does not sag or settle	May settle, reducing efficiency	Some settling over time
Lifespan	50+ years	20-30 years	15-25 years
Fire Resistance	Fire-resistant, varies by product	Non-combustible but melts at high temperatures	Fire-retardant treated
Installation	Easier DIY application with spray kits; no drilling required	Requires drilling into walls and a specialized machine	Requires drilling into walls and a specialized machine
Cost	Higher upfront investment ($0.75−4.50 per sq ft)	Lower ($0.40−1.50 per sq ft)	Moderate ($0.60−2.50 per sq ft)
Best For	High-efficiency homes, basements, crawl spaces	Attics, open wall cavities, retrofits	Wall cavities, soundproofing, eco-friendly projects

Key Takeaways:

• Closed-cell spray foam outperforms blown-in insulation in R-value, moisture resistance, and long-term durability.
• Blown-in fiberglass is affordable but less effective at air sealing and requires drilling into walls and specialized equipment.
• Blown-in cellulose offers better thermal performance than fiberglass but requires better moisture management and precise application to avoid gaps.

Benefits and Drawbacks

Choosing the right insulation type depends on performance, longevity, and cost-effectiveness. While closed-cell spray foam insulation delivers superior R-value, air sealing, and moisture protection, blown-in insulation can be a more budget-friendly solution for large areas like attics. However, both insulation types have advantages and drawbacks depending on the application.

The table below outlines the pros and cons of spray foam vs blown-in insulation, helping you determine which option is best for your needs.

Insulation Type	Pros	Cons
Closed-Cell Spray Foam	- Maximum energy efficiency - Moisture-resistant - Long-lasting durability - Strengthens structures - Easier DIY application with spray kits	- Higher upfront cost - Professional installation recommended for large areas - Difficult to modify or remove
Blown-In Fiberglass	- Affordable upfront cost - Good coverage for large areas - Fire-resistant	- Requires a machine and drilling into walls - Poor air sealing - Absorbs moisture - Can settle over time
Blown-In Cellulose	- Eco-friendly - Better soundproofing - Good thermal performance	- Requires a machine and drilling into walls - Susceptible to moisture damage - Settling reduces effectiveness - Flammability risk

When Should You Choose Closed-Cell Spray Foam vs Blown-In Insulation?

The best insulation choice depends on your priorities—whether it's energy efficiency, budget, moisture resistance, or long-term performance.

Choose Closed-Cell Spray Foam When:

• Maximum energy efficiency is your goal – Higher R-value per inch means better thermal resistance.
• You're insulating moisture-prone areas – Ideal for basements, crawl spaces, and exterior walls.
• You want long-term durability – Spray foam does not degrade or settle over time.
• Structural reinforcement is a priority – The rigid nature of closed-cell foam adds strength to buildings.
• Your budget allows for a higher initial investment – The long-term savings in energy bills can justify the cost.

Choose Blown-In Fiberglass When:

• Affordability is your main concern – One of the most cost-effective insulation solutions.
• You're insulating a large attic or open cavities – Quick and easy installation over a wide area.

Choose Blown-In Cellulose When:

• Eco-friendliness is important – Made from recycled paper, cellulose is a more sustainable option.
• You need better soundproofing – Denser than fiberglass, it helps reduce noise transmission.
• You're retrofitting an older home – Works well in closed wall cavities.

💡 A Hybrid Approach? Some homeowners use closed-cell spray foam for critical moisture-prone areas (like crawl spaces and rim joists) while filling large open areas with blown-in fiberglass or blown-in cellulose insulation to balance performance and cost.

FAQs

How Much Does Spray Foam Insulation Cost?

Costs vary based on type, project size, and installation method. Closed-cell spray foam costs $0.75–$4.50 per sq ft, while open-cell ranges from $0.55–$2.50 per sq ft. For a full breakdown, check out A Complete Guide to Spray Foam Insulation Costs.

Is an R Value Important for Insulation?

Yes! R-value measures thermal resistance—higher R-values mean better insulation. Closed-cell spray foam R-value is one of the highest (5.6-8.0 per inch), making it highly efficient. Learn more in Understanding the Importance of R-Value in Spray Foam Insulation.

How Does Closed-Cell Spray Foam Compare to Batt Insulation?

Spray foam offers better R-value, air sealing, and moisture resistance, while batt insulation is more affordable but less effective in preventing air leaks. See a full comparison in Closed Cell Spray Foam vs Batt Insulation.

How Does Open-Cell Compare to Closed-Cell Spray Foam?

Open-cell foam is softer and better for soundproofing, while closed-cell is denser, with higher R-value and moisture resistance, making it ideal for basements and crawl spaces. Find the best option in Open vs. Closed Cell Explained.

Can Spray Foam and Blown-In Insulation Be Used Together?

Yes! Combining insulation types can optimize both cost and performance. A common approach is to use closed-cell spray foam for air sealing around rim joists, crawl spaces, and moisture-prone areas, then fill larger spaces like attics with blown fiberglass or blown cellulose for cost-effective coverage.

Can I Install Spray Foam Insulation Myself?

Easy-to-use DIY kits for expanding foam insulation are available, but professional installation is recommended for large areas to ensure proper coverage and performance. If using a DIY spray foam insulation kit, follow the instructions carefully.

Which Insulation Is Best for Hard-to-Reach Areas?

For irregular cavities, electrical penetrations, and tight spaces, closed-cell spray foam is the superior choice due to its ability to expand and create a complete air seal. However, for retrofits in attics or closed wall cavities, blown-in insulation is a more practical choice.