Insulation R-value per inch
Quick answer: common insulation ranges from roughly R-2.2 to R-7+ per inch. Fiberglass is commonly about R-2.2–4.3/in depending on form and density; cellulose and mineral wool are generally in the upper R-3s; rigid foam is commonly around R-4 to R-6+; closed-cell spray foam is typically much higher per inch than open-cell foam.
Values below are comparison references, not universal product constants. Exact performance depends on product, density, thickness, temperature, aging, settling, compression, and installation. U.S. units are h·ft²·°F/Btu per inch; metric equivalents use RSI = R × 0.1761 per 25.4 mm.
This three-column comparison is designed to fit phones without page-level horizontal scrolling.
| Insulation | Form | R-value per inch |
|---|---|---|
| Fiberglass — standard density | Batt | R-2.9–3.8/in |
| Fiberglass — high density | Batt | R-3.7–4.3/in |
| Fiberglass | Loose-fill | R-2.2–2.7/in |
| Cellulose | Blown / loose-fill | R-3.6–3.8/in |
| Mineral / stone wool | Batt or loose | ≈ R-3.7/in |
| EPS | Rigid board | R-3.85–4.60/in |
| XPS | Rigid board | ≈ R-5.0/in |
| Polyiso | Rigid board | R-5.6–8.0/in |
| Open-cell spray foam | Spray foam | ≈ R-3.6–3.7/in |
| Closed-cell spray foam | Spray foam | ≈ R-6.5–7.4/in |
R-value per inch at a glance
Range bars are a visual comparison of the primary table—not additional data. Scale: R-0 to R-8 per inch.
Print scope: the primary R-value chart, practical reference tables, existing-attic screening table, and source list.
Approximate thickness for common target R-values
These are planning estimates calculated from the comparison values above. A range means the thickness changes across the stated R/in range. Use exact product labels for final sizing; loose-fill insulation is intentionally excluded because bag coverage and settled depth control installation.
| Material / form | R-30 | R-38 | R-49 | R-60 |
|---|---|---|---|---|
| Fiberglass batt — standard | 7.9–10.3 in | 10.0–13.1 in | 12.9–16.9 in | 15.8–20.7 in |
| Fiberglass batt — high density | 7.0–8.1 in | 8.8–10.3 in | 11.4–13.2 in | 14.0–16.2 in |
| Mineral / stone wool | 8.1 in | 10.3 in | 13.2 in | 16.2 in |
| EPS rigid board | 6.5–7.8 in | 8.3–9.9 in | 10.7–12.7 in | 13.0–15.6 in |
| XPS rigid board | 6.0 in | 7.6 in | 9.8 in | 12.0 in |
| Polyiso rigid board | 3.8–5.4 in | 4.8–6.8 in | 6.1–8.8 in | 7.5–10.7 in |
| Open-cell spray foam | 8.1–8.3 in | 10.3–10.6 in | 13.2–13.6 in | 16.2–16.7 in |
| Closed-cell spray foam | 4.1–4.6 in | 5.1–5.8 in | 6.6–7.5 in | 8.1–9.2 in |
Do not use this table as an order quantity. Board products can have thickness-dependent published R-values, foam performance can vary with tested thickness and formulation, and installed batts must fit the cavity without improper compression.
Common framing cavity depths
Nominal lumber size is not the same as actual cavity depth. This reference helps you judge whether a batt or foam thickness can physically fit before checking the exact product specification.
| Nominal framing | Actual depth | Use |
|---|---|---|
| 2×4 | 3.5 in | Common wall cavity |
| 2×6 | 5.5 in | Deeper wall / roof cavity |
| 2×8 | 7.25 in | Floor / roof framing |
| 2×10 | 9.25 in | Floor / roof framing |
| 2×12 | 11.25 in | Deep floor / roof framing |
Cavity depth does not determine the required R-value and does not guarantee that a product should fill the full cavity. Use the insulation product’s labeled thickness and installation instructions.
How can I estimate the R-value of existing attic insulation?
ENERGY STAR provides simple screening factors for a visual attic check. Multiply the measured insulation depth in inches by the factor below. These values are for quick screening, not product identification or certification.
| What you see | Likely material | Screening factor |
|---|---|---|
| Lightweight yellow, pink, or white loose fibers | Fiberglass | ≈ R-2.5/in |
| Dense gray or near-white fibers, sometimes with black specks | Rock wool | ≈ R-2.8/in |
| Small gray flat pieces or newsprint-like fibers | Cellulose | ≈ R-3.7/in |
| Lightweight granules | Vermiculite / perlite | ≈ R-2.7/in |
| Yellow, pink, or white batts | Fiberglass batt | ≈ R-3.2/in |
Vermiculite caution: ENERGY STAR warns that some vermiculite insulation may contain asbestos. Do not disturb suspect vermiculite unless it has been appropriately tested.
Verified product examples behind the comparison
These examples show why one material family should not be reduced to a single universal number. They are evidence checks, not product endorsements.
| Example | Published thermal value | What it confirms |
|---|---|---|
| Knauf Performance+ EcoBatt | R-13 and R-15 HD at 3.5 in | Fiberglass density/product changes R-value at the same thickness. |
| Greenfiber SANCTUARY | 3.7 R/in at cited settled condition | Loose-fill product data must preserve settled-density and coverage conditions. |
| ROCKWOOL Comfortbatt | R-13 / R-15 at 3.5 in examples | Stone-wool product values vary by product/density. |
| Owens Corning FOAMULAR NGX | R-5 per inch long-term thermal resistance | XPS aged performance should be treated as product-specific. |
| Rmax Durasheath | R-6.0 at 1 in | Polyiso performance is product-, thickness-, and temperature-dependent. |
| Huntsman CLASSIC ULTRA | Aged R-3.7 per inch | Open-cell spray foam is materially lower R/in than closed-cell foam. |
| Huntsman ICYNENE HFO 200 | Aged R-7.4 at 1 in; R-23 at 3.5 in | Closed-cell foam can exceed R-6/in and need not scale perfectly linearly. |
Why can the same insulation material have different R-values?
R-value is a measured thermal resistance, not a fixed material nickname. Density, formulation, installed thickness, compression, mean test temperature, moisture condition, foam aging, and loose-fill settling can all change the reported or installed result.
For most non-reflective home-insulation claims, FTC 16 CFR §460.5 specifies recognized test methods at a 75°F mean temperature and a 50°F ±10°F temperature difference; foam-plastic aging and loose-fill settling also require specific treatment. For final design or purchasing, use the exact product label, fact sheet, and installation conditions.
Worked example: 8 inches of existing cellulose
Using ENERGY STAR’s existing-attic screening factor, an 8 in layer of identified cellulose is approximately 8 × 3.7 = R-29.6. Treat that as a screening estimate. Uneven depth, settling, moisture, disturbance, or uncertainty about the material can make the actual thermal resistance different.
For new loose-fill purchasing, use the manufacturer’s coverage chart and settled-thickness requirements rather than dividing a target R-value by 3.7.
What this chart does not tell you
- Whole-wall or whole-roof R-value: framing and other parallel heat-flow paths reduce assembly performance compared with the insulation layer alone.
- Code compliance: required total R-value depends on jurisdiction, climate zone, assembly, and adopted code. This chart is a material reference, not a code selector.
- Radiant-barrier R/in: reflective systems depend on air space, surface emittance, and heat-flow direction, so a single material R-value per inch is not an honest comparison.
- Exact purchase quantities: loose-fill bag coverage, batt package coverage, board thickness, and spray-foam yield must come from the exact product documentation.
Need an exact insulation calculation?
Use the Insulation Calculator for project area, packages, bags, sheets, spray-foam kits, and cost using exact product coverage. Use the R Value Calculator to convert R-value and RSI or solve thickness from verified thermal conductivity.
Sources and reference scope
The primary comparison combines a U.S. Department of Energy Building America reference table with current product examples where a modern product-specific check adds useful context. ENERGY STAR values are kept separate as existing-attic screening factors. Sources rechecked September 28, 2026.
- U.S. Department of Energy — Building America Best Practices Series, Volume 12 (February 2011)Supports average R-value-per-inch comparison ranges including standard/high-density fiberglass, blown fiberglass, cellulose, mineral wool, XPS, and polyiso.
- U.S. Department of Energy — Building America House Simulation Protocols (Revised)Provides default R/in references including open-cell polyurethane foam at 3.6/in and closed-cell polyurethane foam at 6.5/in; used only as a comparison/default reference, not a current product specification.
- eCFR — 16 CFR §460.5, R-value testsControls the U.S. test basis described on this page, including mean-temperature/difference conditions, foam-plastic aging, and loose-fill settling requirements.
- ENERGY STAR — What to Look For: DIY Checks and InspectionsSupports the separate existing-attic screening factors for fiberglass, rock wool, cellulose, vermiculite/perlite, and fiberglass batts.
- Knauf — Performance+ EcoBatt InsulationSupports the verified R-13 and R-15 HD at 3.5 in fiberglass batt examples.
- Greenfiber — SANCTUARY Cellulose InsulationSupports the cited 3.7 R/in product example and settled-thickness/coverage context.
- ROCKWOOL — Comfortbatt Technical Data SheetSupports current stone-wool batt R-values and thickness examples tested to ASTM C518.
- Insulfoam — Expanded Polystyrene ASTM C578 physical propertiesSupports EPS R-3.85 through R-4.60 per inch at 75°F across cited product types.
- Owens Corning — FOAMULAR NGX product guideSupports the R-5 per inch long-term thermal-resistance example for the cited XPS product line.
- Rmax — Durasheath Product Data Sheet, Rev. 03-05-2025Supports the cited 1 in polyiso example at R-6.0 and its thermal-test conditions.
- Huntsman Building Solutions — CLASSIC ULTRASupports the cited current open-cell spray-foam example at aged thermal resistance R-3.7 per inch.
- Huntsman Building Solutions — ICYNENE HFO 200 Technical Data Sheet (AN 23.00236)Supports the cited closed-cell example: aged R-7.4 at 1 in and R-23 at 3.5 in under ASTM C518.
- Primary units
- U.S. R-value: h·ft²·°F/Btu per inch. Metric equivalents use RSI = R × 0.1761 per 25.4 mm.
- Comparison meaning
- DOE rows are average/reference values; manufacturer rows are product examples. Neither is a substitute for the exact installed product specification.
- Thickness table
- Calculated as target R ÷ stated R/in, rounded to 0.1 in; ranges reverse correctly so the higher R/in produces the smaller required thickness.
- Excluded
- No universal code recommendation, price comparison, whole-assembly R-value, radiant-barrier R/in value, or republished manufacturer coverage dataset.
Common insulation R-value questions
Does compressed fiberglass keep the same R-value?
Not necessarily. Compression changes installed thickness and density, so the exact installed R-value should come from product-specific compressed-cavity data rather than a generic R/in multiplication.
Is spray foam always R-7 per inch?
No. Open-cell and closed-cell formulations differ substantially, and one product can also publish different average R/in behavior at different tested thicknesses. Use the exact product’s aged thermal-resistance data.
Does a radiant barrier have an R-value per inch?
Not as a simple material-only comparison. Reflective-system performance depends on factors including emittance, air-space configuration, and heat-flow direction, so this chart intentionally excludes a universal radiant-barrier R/in number.
Is insulation R-value the same as whole-wall R-value?
No. Material R-value describes the insulation layer. Whole-wall or whole-roof performance also includes framing and other heat-flow paths through the complete assembly.