R-38 at 9.5 in. for wood 16 OC module (15.25 in. × 47 in.)
Key features
Semi-rigid batts with flexible edges for deep cavity contact
Noncombustible stone wool; 0/0 ASTM E84 per manufacturer TDS
Technical specifications
| R-Value | 38.0 |
|---|---|
| Thickness | 9.5 in |
| Width | 15.25 in |
| Length | 47.0 in |
| Coverage | 19.9 sq ft/pack |
| Material | Stone wool (basalt and recycled steel slag) |
| Fire rating | Noncombustible per ASTM E136; Flame Spread 0 / Smoke Developed 0 per ASTM E84 on ROCKWOOL USA Comfortbatt TDS (05-2025). |
| Sound rating | Thick stone wool improves low-frequency damping versus thin cavity fills; STC/NIC still require assembly design. |
| Density | >1.8 lb/ft³ per ASTM C167 on ROCKWOOL USA Comfortbatt TDS (05-2025). |
| Framing width | 16" OC |
| Construction type | Wood stud framing |
| Application area | Attic and cathedral ceilings, high-R exterior wood walls, and exposed floors per ROCKWOOL when 9.5 in. thickness and 15.25 in. × 47 in. module fit the cavity. |
Product details
Aggressive energy codes and above-code programs push attic and roof assemblies toward R-38-class cavity performance without always gifting extra structural depth. A single 9.5 in. stone wool layer can simplify the insulated plane when the framing actually provides ≥9.5 in. of clear cavity for full-thickness batts.
RXCB381525 uses the wood 16 OC module ROCKWOOL publishes as 15.25 in. × 47 in., matching nominal 2×10 or engineered deep cavities when designers size members accordingly—never jam a 9.5 in. batt into a 7-1/4 in. bay.
The Comfortbatt USA sheet (05-2025) places R-38 at 9.5 in. thickness in its thermal resistance table for wood-stud products. Pair that claim with ventilation, air sealing, and wind-washing details in attics; blown caps and smart baffling at eaves still matter.
Fire and durability narratives mirror the family: ASTM E136 noncombustibility and ASTM E84 0/0 indices. In occupied spaces, follow code for ignition barriers and exposed insulation limits.
Logistics: low bag square footage per pack means more wraps per 1,000 square feet of insulated plane—coordinate crane paths, attic hatches, and walkboards before the crew stages pallets.
Submittals should attach https://www.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/residential/comfortbatt-exterior-wood-and-steel-stud-thermal-batt-insulation-techdata-us.pdf dated 05-2025 or newer when ROCKWOOL re-issues.
Documents & certifications
Technical data sheet
Manufacturer-tested R-value, coverage, fire notes, and handling—use for submittals, RFIs, and field QA.
Download PDF (opens in new tab)Certifications & compliance
ASTM C665 Type I compliant, ASTM E136 noncombustible, ASTM E84 flame spread 0 / smoke developed 0 (Note 1 Class A per IBC on TDS), ASTM C518 thermal resistance per published R-thickness table, GREENGUARD Gold per ROCKWOOL Comfortbatt marketing
Frequently asked questions
How many square feet per bag?
How many square feet per bag?
YEARS lists about 19.9 square feet per package for RXCB381525; confirm on the physical master-pack label when ordering pallets.
Can I cut batts for raised-heel truss zones?
Can I cut batts for raised-heel truss zones?
Stone wool is commonly cut with a serrated knife; each piece must still fill its intended cavity without leaving permanent voids or over-compressed channels that kill R-value.
Is R-38 enough for my attic code path?
Is R-38 enough for my attic code path?
IECC attic minimums vary by climate zone and whether the attic is conditioned; compare the labeled product R-value to your jurisdiction’s table and any stretch codes.
Does this replace continuous insulation?
Does this replace continuous insulation?
Cavity batts address stud-bay conduction. Many high-performance walls still use continuous exterior insulation to cut bridging—model the whole envelope.