R-13 at 3.5 in. for 16 in. o.c. wood studs per USA Comfortbatt TDS table
Key features
Same 15.25 in. × 47 in. module class as other wood 16 OC Comfortbatt SKUs
Flexible-edge stone wool; noncombustible with 0/0 ASTM E84 per TDS
Technical specifications
| R-Value | 13.0 |
|---|---|
| Thickness | 3.5 in |
| Width | 15.25 in |
| Length | 47.0 in |
| Coverage | 59.73 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 | Cavity-fill stone wool improves typical acoustics versus empty framing; STC is assembly-dependent. |
| 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 | Exterior wood-framed walls and other Comfortbatt applications where R-13 at 3.5 in. and the 15.25 in. × 47 in. module match the design. |
Product details
Prescriptive energy tables still call for R-13 in nominal 2×4 cavities in some climate and retrofit paths. RXCB351525A packages that target in stone wool rather than lightweight fiberglass when the team wants noncombustible cavity media and the handling story of semi-rigid batts.
Dimensions align with ROCKWOOL’s published wood-stud format: 15.25 in. width × 47 in. length for 16 in. on-center framing, 3.5 in. labeled thickness. The USA Comfortbatt technical data sheet (05-2025) lists R-13 at 3.5 in. thickness in the wood-stud thermal resistance table—use that PDF for inspector-facing language.
Installation quality still dominates outcomes: maintain consistent thickness, split around obstructions without carving permanent voids, and coordinate electrical boxes so insulation is not permanently compressed behind device ears.
Fire documentation matches the broader Comfortbatt family: ASTM E136 noncombustibility and ASTM E84 0/0 indices on the sheet. As always, hourly rated walls need listed assemblies, not the loose batt SKU alone.
Moisture control is a systems problem: Comfortbatt publishes favorable sorption and vapor transmission statements for representative samples, but the WRB, flashing, and interior vapor strategy must still match IECC and your hygrothermal model.
Anchor submittals to https://www.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/residential/comfortbatt-exterior-wood-and-steel-stud-thermal-batt-insulation-techdata-us.pdf and refresh when ROCKWOOL re-issues the sheet.
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
What is the difference between RXCB351525 and RXCB351525A?
What is the difference between RXCB351525 and RXCB351525A?
RXCB351525 is R-15 at 3.5 in. for the wood 16 OC module; RXCB351525A is the R-13 variant in the same nominal thickness and module per ROCKWOOL’s published thermal table. Match the SKU to your energy model and AHJ.
Is 15-1/4 in. the same as 15.25 in. width?
Is 15-1/4 in. the same as 15.25 in. width?
Yes—15-1/4 inches equals 15.25 inches. ROCKWOOL lists15.25 in. × 47 in. for wood studs at 16 in. o.c. on the USA Comfortbatt data sheet.
Will stone wool absorb bulk water?
Will stone wool absorb bulk water?
Manufacturer testing cites low water-vapor sorption for Comfortbatt; liquid water management still requires correct flashing, drainage, and drying potential in the assembly.
Where do I verify recycled content?
Where do I verify recycled content?
Use ROCKWOOL’s environmental product documentation and the current Comfortbatt technical data sheet on rockwool.com for certification and sustainability statements tied to your purchase date.