Spray Foam Insulation
Core spray foam pages that explain material types, costs, R-values, and common alternatives.
Spray Foam vs Fiberglass Insulation
Fiberglass is cheaper upfront. Spray foam performs better for decades. Here's the full picture for Indiana homeowners and building owners.
Quick Answer
Spray foam insulation outperforms fiberglass in nearly every measurable category: higher R-value per inch, complete air sealing, moisture resistance, and a lifespan that matches the building itself versus 15 to 25 years for fiberglass. Fiberglass costs less upfront, but spray foam typically pays for itself through energy savings within 3 to 7 years.
Performance Comparison
| Feature | Spray Foam | Fiberglass |
|---|---|---|
| R-Value per Inch | R-3.6 (open-cell) to R-7.0 (closed-cell) | R-2.5 (loose-fill) to R-3.8 (high-density batts) |
| Air Sealing | Yes — expands to fill every gap and crack | None — air flows freely around and through batts |
| Moisture Resistance | Closed-cell resists water; open-cell allows drying | Absorbs moisture, loses R-value when wet |
| Mold Resistance | Inert polymer — does not support mold growth | Can trap moisture against surfaces, promoting mold |
| Installed Cost (per sq ft, R-19) | $1.50 - $3.50 | $0.50 - $1.20 |
| Lifespan | Life of the building under normal conditions (no settling) | 15 - 25 years (sags, compresses, loses R-value) |
| Installation Quality | Fills every cavity, gap, and irregular shape | Depends on installer precision; gaps are common |
| Energy Savings | 20% - 30% reduction in heating/cooling costs | 10% - 20% reduction (air leakage limits performance) |
| Sound Reduction | Good to excellent (especially open-cell) | Moderate |
| Structural Benefit | Closed-cell adds racking strength to walls | None |
R-Value per Inch
Spray Foam
R-3.6 (open-cell) to R-7.0 (closed-cell)
Fiberglass
R-2.5 (loose-fill) to R-3.8 (high-density batts)
Air Sealing
Spray Foam
Yes — expands to fill every gap and crack
Fiberglass
None — air flows freely around and through batts
Moisture Resistance
Spray Foam
Closed-cell resists water; open-cell allows drying
Fiberglass
Absorbs moisture, loses R-value when wet
Mold Resistance
Spray Foam
Inert polymer — does not support mold growth
Fiberglass
Can trap moisture against surfaces, promoting mold
Installed Cost (per sq ft, R-19)
Spray Foam
$1.50 - $3.50
Fiberglass
$0.50 - $1.20
Lifespan
Spray Foam
Life of the building under normal conditions (no settling)
Fiberglass
15 - 25 years (sags, compresses, loses R-value)
Installation Quality
Spray Foam
Fills every cavity, gap, and irregular shape
Fiberglass
Depends on installer precision; gaps are common
Energy Savings
Spray Foam
20% - 30% reduction in heating/cooling costs
Fiberglass
10% - 20% reduction (air leakage limits performance)
Sound Reduction
Spray Foam
Good to excellent (especially open-cell)
Fiberglass
Moderate
Structural Benefit
Spray Foam
Closed-cell adds racking strength to walls
Fiberglass
None
Why Air Sealing Changes Everything
The single biggest advantage spray foam holds over fiberglass is air sealing. According to the Department of Energy, air leakage accounts for 25% to 40% of heating and cooling energy loss in a typical home. Fiberglass batts are thermal insulators, but they do nothing to stop air movement — wind, stack effect, and pressure differences push conditioned air right through fiberglass. Spray foam expands on contact to seal every gap, crack, and penetration in the building envelope. This is why homes insulated with spray foam consistently test at 2 to 4 ACH50 (air changes per hour at 50 Pascals) on blower door tests, while fiberglass-insulated homes typically measure 6 to 10 ACH50. That difference in air tightness is what drives the 20% to 30% energy savings spray foam typically delivers.
Pros and Cons
Spray Foam Insulation
Pros
- Complete air seal eliminates drafts and reduces energy loss by up to 30%
- Highest R-value per inch of any widely available insulation
- Lasts the life of the building — no settling, no degradation, no replacement cycle
- Closed-cell acts as a vapor and moisture barrier
- Fills irregular cavities, pipes, and wiring penetrations perfectly
- Reduces pollen, dust, and outdoor pollutant infiltration
Cons
- Higher upfront cost ($1.50 - $3.50/sq ft at R-19 vs $0.50 - $1.20 for fiberglass)
- Requires professional installation with specialized equipment
- Must be installed in proper temperature and humidity conditions
- Occupants must vacate during installation and for 24 hours after
Fiberglass Insulation
Pros
- Lowest upfront material and installation cost
- Widely available and familiar to all general contractors
- DIY-friendly for basic batt installations
- Non-combustible (important in some fire-rated assemblies)
Cons
- Zero air-sealing ability — air leaks freely through and around batts
- R-value degrades over time as material sags, compresses, and settles
- Absorbs moisture and loses insulating performance when wet
- Installation quality varies widely — gaps and compression are common
- Must be replaced every 15 to 25 years to maintain performance
- Can trap moisture against framing, contributing to mold and wood rot
Long-Term Cost Analysis
Fiberglass insulation costs roughly $0.50 to $1.20 per square foot installed at R-19, while spray foam runs $1.50 to $3.50 per square foot for equivalent thermal performance. For a 1,500 sq ft attic, that's approximately $750 to $1,800 for fiberglass versus $2,250 to $5,250 for spray foam. However, the Department of Energy estimates that air sealing and proper insulation together save the average homeowner $200 to $600 per year on energy bills. In Indiana, where electricity averages ~$0.14/kWh and natural gas runs ~$1.10/therm (above the national average for gas), the payback math favors spray foam even more strongly — especially for heating-dominated homes. Over a 25-year period, spray foam's energy savings ($5,000 to $15,000) plus avoided replacement costs (fiberglass needs replacing at least once in that span) typically exceed the upfront price difference. Many Indiana homeowners recoup the extra investment within 3 to 7 years.
When to Choose Each Option
Whole-Home Insulation (New Build or Gut Reno)
When walls and cavities are open, spray foam gives you the best long-term performance envelope. The cost premium is smallest during new construction because the cavities are already accessible.
Spray FoamBudget-Constrained Rental Property
If the property will be sold or significantly renovated within 5 years, the energy savings may not offset the upfront cost of spray foam. Fiberglass batts provide baseline insulation at the lowest cost.
Fiberglass (short-term economics favor it)Crawl Spaces and Rim Joists
These areas are exposed to ground moisture and outside air infiltration. Closed-cell spray foam is the only insulation that simultaneously insulates, air-seals, and provides a moisture barrier in these critical zones.
Spray Foam (closed-cell)Supplemental Attic Insulation
If existing fiberglass in an attic is thin or settling, adding blown-in fiberglass or cellulose on top can be cost-effective. But if you're starting from scratch or need air sealing, spray foam on the roofline is superior.
Depends on existing conditionsCommercial Buildings & Retail Spaces
Commercial buildings face higher air infiltration loads due to frequent door openings, large HVAC systems, and complex rooflines. Spray foam's air-sealing capability reduces energy waste significantly in these demanding environments, while fiberglass in commercial drop ceilings and metal stud walls consistently underperforms due to air bypass.
Spray Foam (air sealing ROI is highest in commercial)Our Verdict
Spray foam insulation is the superior performer by every technical measure: R-value, air sealing, moisture resistance, and longevity. The only area where fiberglass wins is upfront cost — and even that advantage disappears within a few years when you account for energy savings and replacement cycles. For homeowners planning to stay in their home for 5 or more years, spray foam is the better long-term investment. For tight budgets or short-term ownership, fiberglass remains a viable option. If you’ve decided on spray foam, see our Open-Cell vs Closed-Cell guide to choose the right type for your project.
Frequently Asked Questions
Most homeowners see a 20% to 30% reduction in heating and cooling costs after upgrading to spray foam, translating to $200 to $600 in annual savings depending on home size, climate, and energy rates. In Indiana (Climate Zone 5), where heating dominates energy bills, savings tend toward the higher end of that range.
It is not recommended. Fiberglass batts should be removed before applying spray foam. Leaving fiberglass in place can trap moisture between the two materials, reduce the spray foam's adhesion to the substrate, and prevent proper inspection of the cavity. Removal adds cost but ensures the spray foam performs as designed.
Fiberglass is not inherently bad — it's a proven thermal insulator that has been used successfully for decades. Its limitations are air sealing (it has none), moisture performance (it degrades when wet), and longevity (it sags and loses R-value over 15 to 25 years). In applications where air sealing and moisture resistance are not critical, fiberglass can be adequate.
Spray foam insulation lasts the life of the building without settling, sagging, or losing R-value. Fiberglass batts typically begin degrading after 15 years and should be replaced every 15 to 25 years to maintain rated performance. Over a 50-year period, you would likely replace fiberglass at least twice while spray foam remains intact.
Yes. Because spray foam creates a complete air seal, it reduces the pathways through which outdoor allergens, dust, pollen, and pollutants enter the home. Homes with comprehensive air sealing have fewer avenues for outdoor contaminants compared to fiberglass, which allows air — and everything it carries — to pass through freely.
Older homes often benefit the most from spray foam because they tend to have the worst air leakage. Homes built before 1980 commonly have little or no air sealing, and retrofitting spray foam in the attic, crawl space, and rim joists can cut energy bills by 30% or more. The payback period for older homes is often shorter than for newer construction.
Commercial buildings typically see an even stronger ROI from spray foam than residential. Higher air infiltration loads from frequent door openings, complex rooflines, and large HVAC systems mean the air-sealing benefit has a bigger impact. Many Indiana commercial building owners report 20% to 30% reductions in heating and cooling costs after spray foam retrofit, with payback periods of 2 to 5 years depending on building size and energy rates.
Related
Related resources
Crawl Space Insulation
Crawl space pages that connect moisture control, closed-cell foam, and residential retrofit planning.
Related Services
Open-Cell Foam
R-3.6 per inch with excellent air sealing and sound dampening. Ideal for new construction, multi-family, and commercial interiors.
- Lowest cost per board foot of any spray foam
- Noticeably quieter, reduces sound between rooms and from outside
- Great for attics, interior walls, and bonus rooms
Closed-Cell Foam
R-6.5 per inch with integrated vapor barrier and structural racking strength. The standard for commercial exteriors, metal buildings, and cold storage.
- Highest R-value of any spray-applied insulation (R-6.5 per inch)
- Acts as a vapor barrier
- Won't absorb water — ideal for moisture-prone areas
Attic Insulation
Stop losing heat through your roof. Attic spray foam targets the biggest source of energy loss in Indiana homes.
- Reduce heating and cooling loads immediately
- Prevent ice dam formation in winter
- Create conditioned attic space when applied to roof deck
Crawl Space Insulation
Seal out moisture, mold, and cold floors. Closed-cell crawl space encapsulation for a dry, energy-efficient foundation.
- Reduce moisture accumulation and mold growth
- Warmer floors above the crawl space in winter
- Stop musty air infiltration into living spaces
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