Spray Foam Insulation Cost (2026 Price Guide)
Part of Interior & Finishes
Quick answer
Spray foam insulation costs roughly $1.00–$1.50 per board-foot installed for open-cell and $1.50–$3.00 for closed-cell (a board-foot is 1 ft² at 1 inch thick). For a 2x4 wall at 3.5 in that's about $3.50–$5 per square foot open-cell, or $5–$10 closed-cell. DIY kits run about $1–$1.50 per board-foot.
Spray foam is priced by the board-foot — one square foot covered one inch thick — because cost scales with thickness, not just area. Closed-cell foam is denser, has a higher R-value per inch (~6.5 vs ~3.7) and costs more; open-cell is cheaper and good for interior walls and sound.
Spray foam cost by type
| Type | R per inch | Cost per board-foot | Best for |
|---|---|---|---|
| Open-cell | ~3.7 | $1.00–$1.50 | Interior walls, attics, sound |
| Closed-cell | ~6.5 | $1.50–$3.00 | Rim joists, basements, exterior, moisture barrier |
Typical project costs
| Project | Area | Closed-cell estimate |
|---|---|---|
| Rim joist (2 in) | 150 ft² | $450–$900 |
| 2x4 wall (3.5 in) | 500 ft² | $2,600–$5,300 |
| Attic deck (5 in) | 1,000 ft² | $7,500–$15,000 |
Use the insulation calculator with the spray-foam option to convert your area and target R-value into board-feet, then multiply by the per-board-foot price above. It also estimates the number of pro kits (about 600 board-feet each) for a DIY job.
What drives the price
- Thickness: cost is per board-foot, so doubling the depth doubles the price.
- Open vs. closed cell: closed-cell is roughly twice the price but gives more R per inch and acts as an air and moisture barrier.
- Access and prep: tight crawlspaces, masking and old-insulation removal add labor.
- DIY kits save labor but cover less than a rig and are harder to apply evenly.
FAQs
Is spray foam worth the extra cost?
Spray foam costs more than batts or blown-in but also air-seals as it insulates, which fiberglass doesn't. For rim joists, vaulted ceilings and hard-to-seal areas the air-sealing is often worth it; for an open attic floor, blown-in usually wins on cost per R-value.
How is spray foam measured and priced?
By the board-foot — one square foot at one inch thick. A 500 ft² wall sprayed 3.5 inches deep is 1,750 board-feet. Multiply board-feet by the per-board-foot price for your foam type to get the cost.