Spray foam wins in a few specific applications. Batts win almost everywhere else. Here's the honest comparison.
Spray foam and batt insulation are the two most common choices for cavity insulation, but they work differently, cost differently, and suit different situations. Understanding the trade-offs helps you choose the right product for each application — and avoid paying a premium where it isn't justified.
| Factor | Spray Foam (Closed Cell) | Fiberglass / Mineral Wool Batts |
|---|---|---|
| R-value per inch | R-6 to R-7 per inch | R-3.2 to R-4.3 per inch |
| Air sealing | Excellent — seals gaps on application | Good, but requires separate air barrier |
| Vapor control | Class II (2") or Class I (3"+) | Kraft-faced = Class II; unfaced = Class III |
| Installation | Requires licensed contractor, PPE | DIY-friendly; quick professional install |
| Cost | Significantly higher per sq ft | Lower cost, especially at volume |
| Rework / change | Difficult — foam bonds to framing permanently | Easy to remove and replace |
| Fire performance | Combustible — requires thermal barrier (drywall) | Fiberglass: noncombustible. Mineral wool: noncombustible |
| Code assemblies | Complex — IBC/IRC require thermal barrier | Standard assemblies well-documented |
| Best for | Rim joists, unvented cathedral ceilings, tight spaces | Walls, attics, floors, most standard cavities |
Spray foam excels in applications where air sealing is critical and the geometry makes batts difficult: rim joists (the single most common spray foam application), unvented cathedral ceiling assemblies where vapor and air control both need to come from the insulation itself, and irregular cavities around HVAC penetrations and oddly-shaped framing. In these specific situations, spray foam's air-sealing performance justifies the cost premium.
For standard stud-bay applications — exterior walls, attic floors, floor joists over crawl spaces — batts deliver the required R-value at dramatically lower cost per bag. There's no air-sealing advantage spray foam can offer in a standard wall that an air barrier membrane plus well-installed batts can't match. Volume pricing on batt orders through a wholesale distributor makes the cost gap even wider.
Many energy-efficient builders use spray foam where it matters most (rim joists, penetrations, unvented roof assemblies) and batts everywhere else. This captures the air-sealing performance advantage of spray foam in the 5% of the building where it's hardest to air-seal any other way, while keeping material costs reasonable on the 95% of cavity insulation where batts are equivalent or better.
We're a batt insulation distributor — we supply fiberglass and mineral wool batts across the full R-value range, wholesale to contractors and builders. If you're building an assembly that uses batts, call (929) 466-1426 for a same-day quote. We don't supply spray foam, but we can help you specify the right batt product for any mixed-insulation assembly.
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