R-Value of Mineral Wool Insulation — Reference Table by Product and Thickness
Mineral wool insulation has an R-value of approximately R-4 per inch, with rigid mineral wool boards ranging from R-4.0 to R-4.3 per inch depending on density. This table covers every mineral wool SKU Warehoos stocks, with R-value, thickness, density, and the ASTM standard used to verify the value.
R-values below are tested per ASTM C518 (steady-state thermal transmission) at 75°F mean temperature, which is the standard reference for building envelope specifications.
Mineral wool R-value reference table
| Product | R-value (per inch) | Common thicknesses | R-value (total) | Density | Standard |
|---|---|---|---|---|---|
| PowerWool RigiBoard (Warehoos exclusive) | R-4.0 | 1.5" / 2" / 3" / 4" | R-6.0 / R-8.0 / R-12.0 / R-16.0 | 8 lb/ft³ | ASTM C518 |
| PowerWool RigiBoard ProMax (Warehoos exclusive) | R-4.0 | 1.5" / 2" / 2.5" / 3" / 4" | R-6.0 / R-8.0 / R-10.0 / R-12.0 / R-16.0 | 11 lb/ft³ | ASTM C518 |
| Rockwool Comfortboard 80 | R-4.2 | 1.25" / 1.5" / 2" / 2.5" / 3" | R-5.25 / R-6.3 / R-8.4 / R-10.5 / R-12.6 | 8 lb/ft³ | ASTM C518 |
| Rockwool Comfortboard 110 | R-4.3 | 1.5" / 2" / 3" | R-6.5 / R-8.6 / R-12.9 | 11 lb/ft³ | ASTM C518 |
| Rockwool Comfortbatt R-15 | R-4.3 | 3.5" (2×4 cavity) | R-15 | 1.7 lb/ft³ | ASTM C518 |
| Rockwool Comfortbatt R-23 | R-4.2 | 5.5" (2×6 cavity) | R-23 | 1.7 lb/ft³ | ASTM C518 |
Quick R-value by thickness (all rigid mineral wool brands)
Rounded to whole numbers for fast reference:
| Thickness | PowerWool RigiBoard | Comfortboard 80 | Comfortboard 110 |
|---|---|---|---|
| 1" | R-4.2 | R-4 | R-4.3 |
| 1.5" | R-6.3 | R-6 | R-6.5 |
| 2" | R-8.4 | R-8 | R-8.6 |
| 2.5" | R-10.5 | R-10 | R-10.75 |
| 3" | R-12.6 | R-12 | R-12.9 |
| 4" | R-16.8 | R-16 | R-17.2 |
R-value vs. fire rating vs. compressive strength
R-value is one of three properties to match against your spec. Mineral wool's full property profile:
| Property | PowerWool RigiBoard | Comfortboard 80 | Comfortboard 110 |
|---|---|---|---|
| R-value per inch | R-4.0 | R-4.2 | R-4.3 |
| Flame Spread Index (ASTM E84) | 0 | 0 | 0 |
| Smoke Developed Index (ASTM E84) | 0 | 0 | 0 |
| Non-combustible per ASTM E136 | ✓ | ✓ | ✓ |
| Compressive strength @ 10% (ASTM C165) | 616 psf | 439 psf | 584 psf |
| Water absorption (ASTM C1763) | <1% by volume | <1% by volume | <1% by volume |
| Vapor permeability | High | High | High |
Choose by R-value AND application: - Exterior continuous insulation (most common) — PowerWool RigiBoard or Comfortboard 80 - Below-grade or high-compression-load — Comfortboard 110 - Cavity insulation in framed walls — Comfortbatt R-15 (2×4) or R-23 (2×6)
IECC climate zone requirements for continuous insulation
The 2024 IECC sets minimum continuous insulation (CI) values for wood-framed walls. Common requirements:
| Climate Zone | Wood-frame wall CI (above cavity) | Mineral wool thickness |
|---|---|---|
| Zone 3 | R-2 to R-3 | 0.5"–0.75" |
| Zone 4 | R-3 to R-5 | 0.75"–1.25" |
| Zone 5 | R-7.5 | 2" |
| Zone 6 | R-7.5 to R-11.25 | 2"–3" |
| Zone 7 | R-11.25 to R-15 | 3"–4" |
| Zone 8 | R-15 | 4" |
These are the R-values added on the exterior of sheathing on top of cavity insulation. Always verify against your jurisdiction's adopted code edition — adoption lags the model code by 1–3 years in most jurisdictions.
Frequently asked questions
Q: What is the R-value of 2 inch mineral wool insulation?
A: PowerWool RigiBoard at 2 inches is R-8.4. Rockwool Comfortboard 80 at 2 inches is R-8. Rockwool Comfortboard 110 at 2 inches is R-8.6. The exact value depends on which product you specify.
Q: What is the R-value of 1 inch mineral wool insulation?
A: Approximately R-4 per inch for rigid mineral wool boards (R-4.0 for PowerWool RigiBoard and PowerWool ProMax, R-4.2 for Comfortboard 80, R-4.3 for Comfortboard 110).
Q: What is the R-value of 3 inch mineral wool insulation?
A: PowerWool RigiBoard at 3 inches is R-12.6. Rockwool Comfortboard 80 at 3 inches is R-12. Rockwool Comfortboard 110 at 3 inches is R-12.9.
Q: What is the R-value of 4 inch mineral wool insulation?
A: PowerWool RigiBoard at 4 inches is R-16.8. Comfortboard 80 at 4 inches is R-16. Comfortboard 110 at 4 inches is R-17.2.
Q: Does mineral wool R-value degrade over time?
A: No. Mineral wool maintains its R-value over its service life. Unlike some closed-cell foams, mineral wool does not contain blowing agents that diffuse out and reduce R-value. The R-value you specify is the R-value you keep.
Q: How does mineral wool R-value compare to fiberglass and rigid foam?
A: Mineral wool is approximately R-4 per inch. Fiberglass batts are R-3.1 to R-4.3 per inch depending on density. Polyisocyanurate (polyiso) rigid foam starts at R-6 per inch but degrades over time. XPS rigid foam is R-5 per inch. EPS rigid foam is R-3.6 to R-4.4 per inch. Mineral wool is competitive with most insulation types while adding fire resistance and moisture management that foam products don't offer.
Q: What R-value do I need for exterior continuous insulation in climate zone 5?
A: 2024 IECC requires R-7.5 continuous insulation for wood-framed walls in climate zone 5. That's approximately 2 inches of mineral wool (R-8 to R-8.6 depending on product). Always verify against your jurisdiction's adopted code edition.
Q: Is the R-value of Comfortboard 110 higher than Comfortboard 80?
A: Slightly. Comfortboard 110 is R-4.3 per inch vs Comfortboard 80 at R-4.2 per inch. The bigger differences are density (110 is 11 lb/ft³ vs 80's 8) and compressive strength (110 handles 584 psf vs 80's 439 psf at 10% deformation, ASTM C165). Choose 110 for below-grade and high-load applications, 80 for typical above-grade continuous insulation. For high-load Warehoos-exclusive options, PowerWool ProMax (11 lb/ft³, >876 psf) exceeds both.
Q: Is the R-value tested at the same temperature for all mineral wool brands?
A: Yes — ASTM C518 specifies 75°F mean temperature as the standard reference. Some manufacturers also report R-value at 40°F mean (R-value rises slightly at lower temperatures). When comparing brands, confirm the test temperature is the same.
Q: Where can I see the official R-value certification for the mineral wool Warehoos sells?
A: Tech data sheets for every SKU we stock are linked from each product page. The PowerWool RigiBoard tech sheet and Rockwool Comfortboard tech sheets are available from the manufacturer or by emailing sales@warehoos.com.
Need mineral wool insulation with verified R-values?
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