Batt insulation (sometimes called batting) carries an R-value of roughly R-2.9 to R-3.7 per inch for standard fiberglass and R-3.6 to R-4.3 per inch for high-density fiberglass and mineral wool. In practice you buy batts by their labeled R-value, not by the inch: a 3.5-inch batt sized for a 2×4 wall reads R-13 or R-15, a 6.25 to 6.5-inch batt reads R-19, and a 12-inch attic batt reads R-38. The number on the bag is what the batt delivers only when it is installed at full thickness in a cavity that matches its depth. Batts also come in set widths and lengths matched to the framing, covered in the sizes section below.
Batt insulation R-value per inch by material
Per inch, batt R-value depends on the fiber and its density. Standard fiberglass (fibreglass outside the U.S.) batts run about R-2.9 to R-3.7 per inch on Owens Corning’s PINK Next Gen submittal (September 2025), from R-19 at 6.5 inches to R-13 at 3.5 inches. High-density fiberglass batts reach about R-3.6 to R-4.3 per inch by packing more glass fiber into the same space. Mineral wool (rock or stone wool) batts sit at about R-4.0 to R-4.3 per inch on ROCKWOOL’s Comfortbatt data sheet, close to high-density fiberglass but with better fire and sound performance.
| Batt material | R-value per inch | Typical use |
|---|---|---|
| Standard-density fiberglass | R-2.9 to R-3.7 | Walls, floors, attic |
| High-density fiberglass | R-3.6 to R-4.3 | 2×6 walls, cathedral ceilings |
| Mineral wool (rock/stone wool) | R-4.0 to R-4.3 | Walls, sound and fire assemblies |
Fiberglass batt R-values (sometimes called the R-factor) are tested to ASTM C665. Because per-inch numbers vary by brand and lot, the labeled R-value on the batt, not a per-inch estimate, is the figure to size your job around.
Batt insulation R-value and thickness chart
Every standard batt R-value maps to a set thickness. Standard fiberglass batts give the familiar R-11, R-13, R-19, R-30, and R-38 grades. High-density fiberglass and mineral wool hit higher R-values (R-15, R-21, R-23) at the same or thinner profiles, which is how a 5.5-inch batt can read R-21 instead of R-19.
| Nominal R-value | Actual thickness | Material type | Designed cavity |
|---|---|---|---|
| R-11 | 3.5 in | Low-density fiberglass | 2×4 wall |
| R-13 | 3.5 in | Standard fiberglass | 2×4 wall |
| R-15 | 3.5 in | High-density fiberglass / mineral wool | 2×4 wall |
| R-19 | 6.25 to 6.5 in (Owens Corning PINK Next Gen: 6.5 in) | Standard fiberglass | 2×6 wall (see compression note) |
| R-21 | 5.5 in | High-density fiberglass | 2×6 wall |
| R-23 | 5.5 in | Mineral wool | 2×6 wall |
| R-25 | 8.25 in | Standard fiberglass | 2×8 floor/ceiling |
| R-30 | 8.25 in (high-density) or 9.5 to 10 in (standard; Owens Corning PINK Next Gen: 9.5 in unfaced or kraft, 10 in FSK-faced) | Fiberglass | 2×8 to 2×10, attic floor |
| R-38 | 10.25 in (high-density) or 12 in (standard) | Fiberglass | 2×10 to 2×12, attic floor |
| R-49 | 14 in | Standard fiberglass | Attic floor, deep trusses |
Sources: Owens Corning PINK Next Gen Fiberglas Insulation submittal sheet, Pub. No. 10024913-C (September 2025); ROCKWOOL Comfortbatt technical data sheet; Insulation Institute (NAIMA) compressed R-value chart, Pub. No. BI506 (10/20), which lists industry label thicknesses of 6.25 in for R-19 and both 9.5 in and 10 in for R-30. Thickness for the same R-value varies by brand, so check the label.
Batts also come in two main widths: 15 inches for framing 16 inches on center, and 23 inches for framing 24 inches on center. Width does not change R-value; it only affects fit and friction hold between studs or joists. For a broader cross-material view, see the full insulation R-value chart by material and climate zone.
Batt insulation sizes and dimensions
Batt insulation dimensions follow the framing. Fiberglass wall batts for wood studs come about 15 or 23 inches wide, to friction-fit framing 16 or 24 inches on center, and 93 or 105 inches long. Attic batts from R-30 up come in 48-inch lengths. Fiberglass batts for steel studs run 16 or 24 inches wide and 96 inches long. Thickness follows the R-value, as the chart above shows.
| Batt | Widths | Lengths |
|---|---|---|
| R-11, R-13, R-15 fiberglass (wood frame) | 15, 15.25, 23 in | 93 or 105 in (R-13 also in 384-in rolls) |
| R-19 fiberglass (wood frame) | 15, 15.25, 19.25, 23 in | 48, 93 or 105 in batts; 470-in rolls |
| R-20, R-21, R-23 fiberglass (wood frame) | 15 in (R-21 also 15.25, 23, 23.25 in) | 93 or 105 in |
| R-30 fiberglass | 15, 16, 19.25, 23, 24 in | 48-in batts; 300-in rolls |
| R-30 and R-38 high-density fiberglass (8.25 and 10.25 in) | 15.5, 23.75 in | 48 in |
| R-38 fiberglass | 16, 19.25, 24 in | 48 in |
| R-49 fiberglass | 16, 24 in | 48 in |
| Fiberglass for metal framing (R-8 to R-25) | 16, 24 in | 96 in (R-19 also 48 in) |
| Mineral wool, wood stud (ROCKWOOL Comfortbatt) | 15.25, 23 in | 47 in |
| Mineral wool, steel stud (ROCKWOOL Comfortbatt) | 16.25, 24.25 in | 48 in |
Sources: Owens Corning PINK Next Gen Fiberglas Insulation product data sheet, Pub. No. 10024567-J (May 2026); ROCKWOOL Comfortbatt technical data sheet (issued 07-2026). Other brands use similar but not identical sizes.
Rolled insulation is the same fiberglass sold as one long blanket you cut to length, and a roll carries the same labeled R-value as a batt of the same grade. Owens Corning’s R-19 roll is 6.25 inches thick and its R-19 batt is 6.5 inches; both are labeled R-19. Rolls suit long joist runs; precut batts suit walls, where every piece is the same height.
The thickest batt in the Owens Corning line is R-49 at 14 inches, and its full range runs from 3.5 inches (R-11) to 14 inches. Width does not change the R-value. Measure the clear space between framing members before you buy and pick the width that fills it.
What R-value batt fits each framing cavity
Match the batt to the cavity depth, not the other way around. A 2×4 wall has a 3.5-inch cavity, a 2×6 wall has 5.5 inches, and deeper floor or ceiling joists take thicker batts. Overstuffing a cavity with a higher-R batt does not add R-value; it compresses the fiber and loses performance.
| Framing | Cavity depth | Best-fit standard batt | Best-fit high-density batt |
|---|---|---|---|
| 2×4 wall | 3.5 in | R-13 | R-15 |
| 2×6 wall | 5.5 in | R-19 (a 6.25-inch R-19 compresses to ~R-18) | R-21 or R-23 |
| 2×8 joist | 7.25 in | R-25 | R-30 (high-density) |
| 2×10 joist | 9.25 in | R-30 | R-38 (high-density) |
| 2×12 joist | 11.25 in | R-38 | R-38 |
The 2×6 wall is where batt choice matters most. An R-19 fiberglass batt is 6.25 to 6.5 inches thick depending on brand, so it gets squeezed into a 5.5-inch cavity; the Insulation Institute chart rates a 6.25-inch R-19 at about R-18 there. An R-21 high-density batt is built at 5.5 inches and holds its full rating in the same wall, which is why many builders spec R-21 over R-19 in 2×6 framing. To shop by product, compare attic insulation rolls by size and brand.
Fiberglass vs mineral wool batt R-value
Mineral wool batts deliver a higher R-value per inch than most standard fiberglass, roughly R-4.0 to R-4.3 versus R-2.9 to R-3.7, so they reach R-15 in a 2×4 wall and R-23 in a 2×6 wall where standard fiberglass tops out at R-13 and R-19. Mineral wool is also denser, does not sag, resists fire to about 1,800 F, and blocks more sound. It costs more per square foot than fiberglass.
Fiberglass batts are cheaper, lighter, and easier to cut, which keeps them the default for most walls and attics. If you need maximum R-value in a fixed cavity, a fire-rated assembly, or quieter interior walls, mineral wool earns the premium. Compare the two directly in fiberglass batts versus blown-in fiberglass.
Standard vs high-density batts
High-density batts pack more fiber into the same thickness, so they hit a higher R-value without a thicker profile. A standard 3.5-inch fiberglass batt reads R-11 or R-13; a high-density 3.5-inch batt reads R-15. In a 2×6 cavity, high-density fiberglass reaches R-21 at 5.5 inches while standard fiberglass needs 6.25 to 6.5 inches to reach R-19.
- Use standard batts when the cavity depth already matches the R-value you need and cost is the priority.
- Use high-density batts when you want the highest R-value a fixed cavity can hold, such as a 2×4 exterior wall or a 2×6 wall where R-19 would compress.
- Use mineral wool when fire rating, sound control, or the highest per-inch R-value drives the choice.
The compression penalty: why the label is not always the R-value
Compressing a batt lowers its R-value, and manufacturers’ instructions call for installation without compression to reach the labeled R-value. The Insulation Institute’s compressed R-value chart (Pub. No. BI506) shows the loss for standard batts squeezed into common framing depths. The trapped air that does the insulating gets pushed out, so a thicker batt in a tight space never delivers its label rating. The chart does not estimate an R-19 crammed into a 3.5-inch 2×4 cavity at all, and warns against extrapolating.
| Batt (rated) | Full thickness | Compressed into | Effective R-value |
|---|---|---|---|
| R-19 fiberglass | 6.25 in | 5.5 in (2×6) | ~R-18 |
| R-30 fiberglass | 10 in | 7.25 in (2×8) | ~R-25 |
| R-30 fiberglass | 10 in | 9.25 in (2×10) | ~R-29 |
| R-38 fiberglass | 12 in | 9.25 in (2×10) | ~R-32 |
| R-49 fiberglass | 14 in | 11.25 in (2×12) | ~R-42 |
Source: Insulation Institute (NAIMA), Estimated R-values for Compressed Fiber Glass Batt Insulation, Pub. No. BI506 (10/20). Industry aggregate values; manufacturer data for a specific product takes precedence.
Two rules follow from this. First, never cram a thicker batt into a shallow cavity to gain R-value; buy the batt built for that depth. Second, a partially compressed higher-R batt can still edge out a lower-rated batt in the same cavity, per the Insulation Institute compressed R-value data: a 10-inch R-30 pressed into a 7.25-inch 2×8 cavity rates about R-25, against about R-24 for an 8-inch R-25 batt in the same cavity.
Does faced or unfaced batt change the R-value?
Facing does not change a batt’s R-value. A kraft-paper or foil facing is a vapor retarder and a stapling flange, not insulation, so an R-13 faced batt and an R-13 unfaced batt insulate the same. Choose faced batts where code requires a vapor retarder on the warm side, and unfaced batts for a second attic layer or where a separate vapor barrier is used.
Attic floors that already have one insulated layer should get unfaced batts on top, laid perpendicular to the joists, so no second vapor retarder is trapped in the assembly.
What R-value batt do you actually need?
The R-value you need depends on the assembly and your climate zone, not on the batt alone. The U.S. Department of Energy recommends R-13 to R-21 for walls and R-25 to R-30 for floors, and ENERGY STAR’s retrofit table recommends R-30 for an uninsulated attic in zone 1, R-49 in zones 2 and 3, and R-60 in zones 4 through 8. Batts can reach the wall and floor targets in a single layer; attic targets above R-38 usually need a second layer or blown-in insulation on top. Our comparison of blown-in insulation vs batts covers which fits an attic better.
| Assembly | Recommended R-value (DOE; ENERGY STAR for attics) | Typical batt solution |
|---|---|---|
| 2×4 exterior wall | R-13 to R-15 | R-13 standard or R-15 high-density |
| 2×6 exterior wall | R-19 to R-21 | R-21 high-density |
| Floors over unconditioned space | R-25 to R-30 | R-30 batt in 2×10 joists |
| Attic (zone 1) | R-30 | R-30 batt |
| Attic (zones 2 and 3) | R-49 | R-49 batt, or R-30 plus a cross layer of R-19 |
| Attic (zones 4 to 8) | R-60 | R-38 batt plus blown-in top-up |
For attic floors, compare batt grades directly in R-30 vs R-38 insulation, and size the full assembly by climate zone with the attic insulation guide by zone and cost. If you are matching an exact thickness, see how thick R-19 insulation is by material. If batts are not settled yet, weigh them against other insulation types in our best insulation for attic guide.
Frequently asked questions
What is the R-value of batt insulation per inch?
Standard fiberglass batt insulation delivers about R-2.9 to R-3.7 per inch. High-density fiberglass and mineral wool batts reach about R-3.6 to R-4.3 per inch. Because per-inch figures vary by brand and density, size a job by the labeled R-value on the batt rather than multiplying a per-inch estimate by thickness.
How thick is R-13, R-19, and R-30 batt insulation?
An R-13 fiberglass batt is 3.5 inches thick and fits a 2×4 wall. An R-19 batt is 6.25 to 6.5 inches thick depending on brand (Owens Corning’s current PINK Next Gen lists 6.5 inches). An R-30 batt is about 8.25 inches in high-density form or 9.5 to 10 inches in standard fiberglass (9.5 inches for Owens Corning unfaced and kraft-faced), used in 2×8 to 2×10 joists and attic floors.
Is R-13 or R-19 better for a 2×4 wall?
R-13 is the correct batt for a 2×4 wall. The cavity is only 3.5 inches deep, so a 6.25 to 6.5-inch R-19 batt would be crushed to little more than half its thickness and lose much of its rating, wasting the material and money. To gain R-value in a 2×4 wall without changing framing, use a high-density R-15 batt built at 3.5 inches.
Can you compress batt insulation to fit a cavity?
Compressing a batt lowers its R-value, so it should be avoided for gaining performance. The Insulation Institute’s chart rates a 6.25-inch R-19 squeezed into a 5.5-inch 2×6 cavity at about R-18, and does not estimate deeper compression such as an R-19 forced into a 3.5-inch cavity. Light compression to fit around wiring is acceptable, but you should never stuff a thicker batt into a shallow space expecting its full rating. Buy the batt sized for the cavity depth.
What R-value batt fits a 2×6 wall?
A 2×6 wall has a 5.5-inch cavity. An R-19 fiberglass batt is 6.25 to 6.5 inches and a 6.25-inch R-19 compresses to about R-18, so many builders instead use a high-density R-21 batt built at 5.5 inches, which holds its full rating. Mineral wool R-23 batts also fit a 2×6 wall at 5.5 inches for the highest single-layer value.
Does a faced batt have a higher R-value than unfaced?
No. Facing is a vapor retarder and stapling flange, not insulation, so a faced and unfaced batt of the same rating insulate identically. Use faced batts where code requires a warm-side vapor retarder, and unfaced batts for a second attic layer or where a separate vapor barrier already exists.
Reviewed by The Roofing Brief Team. Last reviewed: October 2026.