Spray foam vs. fiberglass insulation: which is right for your home?

Choosing between spray foam and fiberglass insulation is one of the most common decisions homeowners face during an insulation project. Both materials insulate effectively, but they work differently, cost differently, and perform better in different situations.

This guide compares the two options head-to-head so you can make a confident decision based on your project, your budget, and your home’s specific needs.

Quick comparison: spray foam vs. fiberglass

Spray foam insulation: pros, cons, and cost

Spray foam insulation is applied as a two-part liquid mixture that expands on contact, filling cavities and creating a continuous layer with no gaps or seams. It comes in two types, each with distinct properties.

Closed-cell spray foam

Closed-cell foam is the highest-performing insulation material commonly available. At R-6.0 to R-7.0 per inch, it delivers more than double the R-value of fiberglass. Its dense, rigid structure also adds structural strength to walls and acts as a moisture vapor barrier.

Cost: $1.50 to $3.50 per square foot installed.

Best applications: crawl spaces, basements, rim joists, exterior walls with limited cavity depth, and areas prone to moisture.

Open-cell spray foam

Open-cell foam is softer, lighter, and less expensive than closed-cell. It provides R-3.5 to R-3.7 per inch, which is comparable to cellulose blown-in insulation. It expands more during application, making it effective for filling large cavities completely.

Cost: $0.75 to $2.00 per square foot installed.

Best applications: interior walls (especially for sound reduction), attic roof decks when creating conditioned attic space, and areas where moisture barriers are not needed.

Spray foam pros

• Superior air sealing. Spray foam fills every crack, gap, and void as it expands. This eliminates the air leakage that undermines other insulation types.
• Highest R-value per inch. Closed-cell spray foam requires the least thickness to reach a given R-value, making it ideal for spaces with limited depth.
• Moisture protection. Closed-cell foam acts as a vapor barrier, preventing condensation problems in walls, crawl spaces, and basements.
• Long-term stability. Spray foam does not settle, sag, or lose R-value over time.
• Structural benefit. Closed-cell foam adds racking strength to walls and roofs.

Spray foam cons

• Higher upfront cost. Spray foam costs two to three times more per square foot than fiberglass.
• Professional installation required. Spray foam requires specialized equipment, chemicals, and training. It is not a DIY project.
• Off-gassing during installation. The chemicals used in spray foam produce fumes during application. Occupants must vacate the home for 24 to 72 hours during and after installation.
• Difficult to modify. Once cured, spray foam is hard to remove if you need access to wiring, plumbing, or framing behind it.
• Inconsistent quality risk. Improperly mixed or applied spray foam can fail to cure correctly, leading to odor issues and poor performance. Hiring an experienced, certified contractor is critical.

Fiberglass insulation: pros, cons, and cost

Fiberglass insulation is the most widely used insulation material in American homes. It is available as batts (pre-cut panels) and loose-fill (blown-in), but for this comparison we focus primarily on batts since blown-in is a separate category. For blown-in pricing, see our blown-in insulation cost guide.

Fiberglass batts

Fiberglass batts are manufactured in standard widths to fit between wall studs and ceiling joists spaced 16 or 24 inches apart. They provide R-2.2 to R-2.7 per inch, and common thicknesses range from R-11 (3.5 inches for 2x4 walls) to R-38 (12 inches for attic floors).

Cost: $0.50 to $1.50 per square foot installed.

Best applications: new construction wall cavities, attic floors with uniform joist spacing, and DIY projects where accessibility is good.

Fiberglass pros

• Lowest upfront cost. Fiberglass batts are the most affordable insulation option available.
• Widely available. Every home improvement store and insulation supplier stocks fiberglass batts in standard sizes.
• DIY friendly. Batts can be installed by homeowners with basic tools and safety equipment.
• Non-combustible. Fiberglass does not burn, though the kraft paper facing on some batts is combustible.
• No off-gassing. Fiberglass does not emit chemicals after installation.
• Extremely long lifespan. When kept dry and undisturbed, fiberglass can last 80 to 100 years.

Fiberglass cons

• No air sealing. Fiberglass does not stop air movement. Wind washing, convective looping, and air leaks around penetrations all reduce its real-world performance.
• Gaps and compression. Batts must be cut precisely around wiring, pipes, and outlets. Gaps as small as 5% of the surface area can reduce overall effectiveness by 25% or more.
• Moisture vulnerability. Wet fiberglass loses nearly all its insulating value. It can take a long time to dry out, and prolonged moisture exposure promotes mold growth.
• Settling (blown-in). Blown-in fiberglass can settle over time, though less than cellulose.
• Irritating to handle. Fiberglass fibers irritate skin, eyes, and lungs during installation. Protective equipment is essential.

When to choose spray foam

Spray foam is the better choice in situations where air sealing matters most and where the higher cost is justified by superior performance.

Crawl spaces and basements

These areas are prone to moisture infiltration and air leakage. Closed-cell spray foam provides insulation, air sealing, and moisture protection in a single application, making it the ideal material for below-grade and semi-exposed spaces.

Rim joists and band joists

The rim joist (where the floor framing meets the foundation wall) is one of the leakiest areas in most homes. Spray foam seals and insulates this junction far more effectively than fiberglass batts, which leave gaps and do not stop air movement.

Cathedral ceilings and finished attics

When the attic is conditioned living space, insulation goes between the rafters rather than on the attic floor. Spray foam applied to the underside of the roof deck creates a continuous air and thermal barrier that fiberglass batts cannot match in this application.

Limited cavity depth

In walls with shallow cavities (2x4 framing, for example), closed-cell spray foam’s R-6.0 to R-7.0 per inch delivers significantly more insulation than fiberglass’s R-2.2 to R-2.7 per inch within the same space.

When to choose fiberglass

Fiberglass is the practical choice for large, accessible areas where air sealing can be handled separately and budget is a priority.

Attic floors

Standard attic floors with good access are fiberglass territory. Blown-in fiberglass or batts layered to the desired depth deliver effective insulation at a fraction of spray foam’s cost. Air sealing the attic floor penetrations before installing fiberglass gives you strong performance without the spray foam price tag.

New construction walls

During new construction, wall cavities are open and accessible. Fiberglass batts fit easily between studs and are the industry standard for this application. Combined with a properly installed air barrier (house wrap, taped sheathing), fiberglass walls perform well.

Budget-conscious projects

When the total budget is limited, fiberglass lets you insulate more area for less money. Insulating your entire attic with fiberglass is almost always better than insulating half of it with spray foam.

DIY installations

If you are comfortable doing the work yourself, fiberglass batts in an accessible attic are a manageable DIY project. The material cost savings are significant, and the installation, while tedious, does not require specialized equipment.

Cost comparison by project

Here is what each insulation type costs for common residential projects.

For full project pricing details, see our blown-in insulation cost guide.

Long-term value: which saves more money?

Both insulation types reduce energy bills, but the long-term value equation is more nuanced than upfront cost alone.

Energy savings comparison

In controlled laboratory settings, spray foam and fiberglass with equivalent R-values perform similarly. In real-world installations, spray foam typically outperforms because its air-sealing properties eliminate the convective air leaks that undermine fiberglass.

Studies by Oak Ridge National Laboratory have shown that fiberglass batts installed in real homes often deliver only 60% to 80% of their rated R-value due to installation imperfections and air movement through the material. Spray foam performs closer to its rated value because it fills gaps completely and stops air movement.

When spray foam’s premium pays off

The extra cost of spray foam is most justified in these scenarios:

• Leaky older homes where air infiltration is the primary energy problem
• Extreme climates where heating and cooling costs are high and every R-value point matters
• Long-term ownership where you will benefit from decades of higher energy savings
• Specific applications like crawl spaces and rim joists where fiberglass simply does not perform well

When fiberglass delivers better value

Fiberglass is the better value when:

• Air sealing is done separately before insulation installation
• Budget is limited and you need to cover maximum area
• The attic floor is the primary target and the space is well-ventilated
• You are selling the home soon and need cost-effective improvements with visible energy savings

The hybrid approach

Many insulation contractors recommend a hybrid strategy: spray foam in targeted areas where air sealing matters most (rim joists, crawl spaces, around windows), combined with fiberglass or blown-in insulation for large open areas like attic floors. This approach captures most of spray foam’s performance benefits at a fraction of the cost of spray-foaming the entire home.

Find insulation contractors near you

Not sure which insulation type is right for your project? A qualified insulation contractor can assess your home’s specific needs and recommend the best approach. Get free quotes from local pros in your area:

• Utah | Salt Lake City
• Idaho | Boise
• Colorado | Denver
• Oregon | Portland
• North Carolina | Charlotte | Raleigh
• Tennessee | Nashville
• Florida | Tampa
• Arizona | Phoenix
• Ohio | Columbus

Frequently asked questions

For more on attic-specific insulation advice, read our attic insulation guide. To understand R-values and what your climate zone requires, visit our R-value guide. For wall projects, see our wall insulation retrofit guide. Or return to our main insulation contractor hub to find qualified pros near you.