R-value per inch by insulation material
This is our own cross-material reference. For every common insulation it pairs the labeled published R/inch band with a derivation unique to this site — the inches of material needed to reach the three attic targets homeowners ask for (R-30, R-38, R-49), computed from required thickness = target R ÷ R/inch at the band midpoint — plus the labeled installed cost band. It is a dated snapshot of stable typicals, not a live feed. See how it’s derived in the methodology, and use it with the R-value calculator and the insulation thickness calculator.
| Material | R / inch | in → R-30 | in → R-38 | in → R-49 | Installed $/ft² |
|---|---|---|---|---|---|
| Fiberglass batt Cheapest; watch gaps and compression | R3.1–R3.4 | 9.2" | 11.7" | 15.1" | $0.80–$2.40 |
| Blown fiberglass Loose-fill; settles a little over time | R2.2–R2.7 | 12.2" | 15.5" | 20.0" | $1.00–$2.80 |
| Cellulose Denser, less air movement; recycled paper | R3.2–R3.8 | 8.6" | 10.9" | 14.0" | $1.00–$2.60 |
| Mineral wool (Rockwool) Fire and water resistant; good acoustics | R3.0–R3.3 | 9.5" | 12.1" | 15.6" | $1.40–$4.00 |
| Open-cell spray foam Air-seals; needs more depth for R | R3.5–R3.7 | 8.3" | 10.6" | 13.6" | $1.00–$2.50 |
| Closed-cell spray foam High R/inch; adds rigidity, low perm | R6.0–R7.0 | 4.6" | 5.8" | 7.5" | $1.50–$4.50 |
| Rigid EPS Lowest-cost rigid board | R3.6–R4.2 | 7.7" | 9.7" | 12.6" | $1.50–$3.50 |
| Rigid XPS Mid rigid board; moisture resistant | R4.5–R5.0 | 6.3" | 8.0" | 10.3" | $1.50–$3.50 |
| Rigid polyiso Highest rigid R; drops in cold temps | R5.6–R6.5 | 5.0" | 6.3" | 8.1" | $1.50–$3.50 |
Labeled planning typicals — R/inch depends on install quality, framing / thermal bridging, moisture and settling; confirm on the product data sheet, and get itemized quotes from licensed, insured insulation contractors. Inches are derived at the band midpoint via required thickness = target R ÷ R/inch. Snapshot: 2026-07-11.