When deciding between spray foam and fiberglass insulation, the choice comes down to performance, cost, and application. Spray foam offers superior air sealing and energy efficiency, but it comes with a higher upfront cost. Fiberglass, on the other hand, is more affordable and easier to install, though it doesn’t seal air leaks as effectively.

This article breaks down the key differences, technical specs, pros and cons, and cost comparisons to help you make an informed decision. Use this guide to understand which insulation type suits your building’s thermal, acoustic, and financial needs.

Insulation Types and How They Compare

Below is a side-by-side comparison of spray foam and fiberglass insulation across key performance and cost factors.

Comparison Table: Spray Foam vs Fiberglass Insulation

Feature	Spray Foam	Fiberglass
Thermal Resistance (R-value)	High (R-6 to R-7 per inch)	Moderate (R-2.2 to R-3.8 per inch)
Air Sealing	Excellent	Poor
Moisture Barrier	Closed-cell resists moisture	Absorbs moisture, may support mold
Installation	Requires professionals	DIY-friendly
Lifespan	80+ years	15–30 years
Cost per Square Foot	$1.00–$3.00 (open-cell) / $1.75–$4.00 (closed-cell)	$0.40–$1.00
Soundproofing	High (closed-cell)	Moderate
Environmental Impact	Higher (chemical-based)	Lower (often contains recycled materials)
Fire Resistance	Needs fire barrier coating	Naturally non-combustible
Energy Savings	Up to 50% on heating/cooling bills	10–25% energy savings

Technical Specifications

Specification	Spray Foam (Closed-cell)	Spray Foam (Open-cell)	Fiberglass (Batt)
R-value per Inch	R-6.5–R-7.0	R-3.5–R-3.6	R-2.9–R-3.8
Density (lb/ft³)	~2.0	~0.5	~0.5–1.0
Permeability (perm)	<1 (vapor barrier)	>10 (not a vapor barrier)	Varies (not air-tight)
Expansion Rate	30x initial volume	100x initial volume	N/A
Application Temp.	40°F–120°F	40°F–120°F	Not temperature-sensitive

Cost Comparison and Market Trends

Spray foam insulation is significantly more expensive up front. However, it often reduces HVAC costs long-term. The U.S. Department of Energy reports that sealing air leaks and insulating properly can save homeowners 15% on heating and cooling bills on average, with spray foam offering the highest ROI in extreme climates.

Installation Costs (Per Square Foot)

Type	Material Cost	Installed Cost
Spray Foam (Open-cell)	$0.50–$1.20	$1.00–$2.00
Spray Foam (Closed-cell)	$1.00–$2.00	$1.75–$4.00
Fiberglass Batt	$0.30–$0.60	$0.40–$1.00

Bonus Tip: Closed-cell spray foam adds structural strength to walls and can increase shear strength by up to 300%, making it a dual-purpose investment in high-wind areas.

Things to Consider Before Making a Decision

Several pre-decision factors will determine which insulation type is right for your space:

• Climate Zone: In colder climates, higher R-value insulation like spray foam offers long-term energy savings. In milder zones, fiberglass may suffice.

• Building Age: Older buildings often benefit from spray foam due to its air-sealing capability.

• Budget Constraints: Fiberglass is best for lower initial investment. Spray foam pays off in lower utility costs but requires higher upfront spending.

• Moisture Exposure: In damp areas like basements, closed-cell spray foam prevents water intrusion better than fiberglass.

• Access to Cavities: Spray foam is ideal for hard-to-reach areas or retrofits where removing drywall isn’t practical.
  Bonus Tip: For mixed applications, consider using spray foam in crawl spaces and attics, and fiberglass in interior walls to balance cost and efficiency.

Common Questions

Can I combine both types of insulation?

Yes. A hybrid approach—spray foam in exterior walls and fiberglass in interior partitions—is common to reduce costs while maintaining performance.

Which insulation is safer?

Fiberglass is naturally fire-resistant and doesn’t emit harmful gases. Spray foam must be installed properly and requires fire-retardant coatings for safety.

Is spray foam environmentally friendly?

Spray foam uses chemicals with high embodied energy, though newer low-GWP formulas are emerging. Fiberglass often includes recycled glass, making it more eco-friendly overall.

Which insulation lasts longer?

Spray foam can last 80+ years with minimal degradation. Fiberglass can sag over time and may need replacement after 15–30 years, especially in humid conditions.

Bonus Tip: Use thermal imaging before and after installation to confirm effective coverage and spot weak areas.

Topic FAQ

Does spray foam really save money on energy bills?

Yes. Spray foam reduces air leakage, which is a major source of energy loss. Homeowners can see up to 50% savings in extreme climates.

Can fiberglass insulation grow mold?

If exposed to moisture, fiberglass can trap water and support mold growth, especially if installed improperly or without vapor barriers.

Is DIY spray foam a good idea?

No. Improper application can result in off-ratio foam, poor adhesion, or even structural damage. Professional installation is strongly recommended.

How thick should spray foam be?

For closed-cell foam, 2–3 inches is typically enough to act as both insulation and vapor barrier. Open-cell may require 4–5 inches for similar performance.

How do I know which insulation is best for me?

Consider your climate, moisture exposure, budget, and energy goals. Spray foam offers performance; fiberglass offers affordability and ease of use.

Make the Right Decision

Spray foam excels in performance, durability, and energy savings—ideal for long-term efficiency and challenging environments. Fiberglass remains a cost-effective, accessible choice for standard insulation needs.

Choose based on your climate zone, building design, and investment horizon. Evaluate both immediate costs and long-term operating expenses to ensure your insulation decision aligns with your goals.

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