Insulation R-Value Chart — R per Inch for Common Materials
Published R-value per inch for fiberglass, mineral wool, cellulose, EPS, XPS, polyiso and spray foam — DOE and manufacturer-verified ranges with aged values.
Updated August 18, 2026
R-value per inch is how insulation materials compete on equal footing: multiply by the installed thickness and you have the layer’s thermal resistance. The catch is that a single material does not have a single number — fiberglass spans 2.2 per inch blown loose in an attic to 4.3 in a high-density batt, purely on density. The table therefore publishes verified ranges, following DOE loose-fill data and manufacturer datasheets, with the typical form each range assumes. Loose-fill figures are settled values, which is what you own a decade after installation.
Foam boards need one extra caution: the label and the long-term value diverge. Polyiso and XPS are blown with gases that slowly diffuse out and get replaced by air, dragging conductivity toward the aged value — polyiso labels around R-6.0–6.5 per inch (LTTR) but NRCA recommends designing at 5.7, and XPS labels 5.0 while its own manufacturer warranty only promises 90% of that (R-4.5). The notes column carries those aged figures so a wall designed today still meets its target in twenty years.
R-Value per Inch — Published Ranges at 75 °F Mean
| Material | R per inch (hr·ft²·°F/Btu) | Notes |
|---|---|---|
| Fiberglass batt | 3.1–4.3 | Standard batts ≈3.1–3.7 (R-11/R-13 in a 3.5 in bay); high-density R-15 batts reach 4.3 |
| Mineral wool (rock wool) batt | 3.1–4.3 | Stone-wool batts; R-15 at 3.5 in (4.3/in) tops the range |
| Cellulose, loose-fill (blown) | 3.2–3.8 | Settled value (DOE loose-fill data); dense-pack wall installs land in the same band |
| Fiberglass blown, attic (loose-fill) | 2.2–2.7 | Settled value at typical open-attic densities of 0.5–1.0 pcf |
| Fiberglass blown, dense-pack wall | 3.7–4.3 | Blown to wall density; achieves R-15 in a 3.5 in stud bay |
| EPS board (expanded polystyrene) | 3.6–4.2 | Rises with density; Type I ≈3.85 at 75 °F. Air-blown, so it does not age-drift |
| XPS board (extruded polystyrene) | 5.0 | Labeled value (ASTM C578). Drifts as blowing agent escapes — warranted minimum is 90% ≈ R-4.5/in aged |
| Polyisocyanurate board (foil-faced) | 5.6–6.9 | Labeled LTTR, typically 6.0–6.5. NRCA in-service design value 5.7/in, and 5.0/in for cold climates |
| Spray foam, closed-cell (ccSPF) | 5.5–7.0 | Typical labels 6.0–6.5/in; value depends on blowing agent and ages like other captive-gas foams |
| Spray foam, open-cell (ocSPF) | 3.5–3.8 | Air/water-blown at ≈0.5 pcf, so no aging drift; ≈3.6/in typical. Vapor-open |
Per-inch resistance at 75 °F mean temperature, as published. Ranges reflect real product and density spreads — use the label of the actual product for compliance, and for loose-fill follow the bag-label coverage chart (bags per 1,000 ft² at the target R), which already accounts for settling. Foam-board aged values matter for design life: polyiso also loses R below ~50 °F mean, the reverse of fibrous materials.
Sources & Further Reading
- DOE/GO-10095-060 "Loose-Fill Insulations" (May 1995) and PNNL Building America Solution Center — settled R/inch for blown cellulose (3.2–3.8) and attic fiberglass (2.2–2.7)
- DOE Energy Saver insulation-materials pages (2016 archive; the live pages have been retired) and InspectAPedia R-value table — batt and generic material ranges
- Manufacturer datasheets: Owens Corning FOAMULAR 250 (XPS R-5.0/in per ASTM C578; lifetime warranty at 90% of labeled), ROCKWOOL ComfortBatt, Johns Manville Spider Plus (dense-pack R-15 @ 3.5 in), EPS-IA Type I data (≈3.85 @ 75 °F)
- PIMA performance bulletin (foil-faced polyiso 5.6–6.9/in LTTR), Building Science Corp. Info-502 and NRCA (Professional Roofing, 2016) — polyiso labels vs in-service 5.7/in; EPS-IA 2016 bulletin on XPS thermal drift
Frequently Asked Questions
Why does the same fiberglass score 2.2 in an attic and 4.3 in a batt?
Density. Blown loose at half a pound per cubic foot, the fiber matrix is open enough for convective loops and radiation to leak heat through it; packed into a high-density batt the same glass fiber traps air in far smaller pores. R per inch climbs steadily with density until the solid fiber itself starts conducting — which is why dense-pack wall fiberglass (3.7–4.3) nearly doubles the attic figure.
Should I design with labeled or aged R for foam boards?
Aged. Polyiso and XPS are blown with low-conductivity gases that diffuse out over years and get replaced by air. Polyiso labels R-6.0–6.5 per inch as LTTR, but NRCA recommends designing at 5.7 — and 5.0 in cold climates, where polyiso additionally loses R at low mean temperatures. XPS labels 5.0, and its manufacturer warranty only stands behind 90% of that. EPS and open-cell spray foam are air-blown and do not drift.
Is total R just R-per-inch times thickness?
For the insulation layer itself, yes — at the rated mean temperature and installed density. The wall or ceiling as a whole is another matter: framing short-circuits the cavity insulation (a wood stud runs about R-1.2 per inch), so the assembly U-value must be area-weighted across studs, headers, and cavities. That whole-assembly step is what a U-value calculation does.
Do loose-fill numbers already include settling?
The DOE ranges quoted here are settled values, and bag-label coverage charts are required by the FTC R-value rule to state initial installed thickness AND the settled thickness that delivers the labeled R. Follow the bag chart’s minimum weight per square foot rather than eyeballing depth — blowing the right depth at too low a density gives you the thickness without the R.
Try the Calculators
Insulation R-Value Chart — R per Inch for Common Materials — reuven.tools/reference/insulation-r-values — verified against: DOE/GO-10095-060 "Loose-Fill Insulations" (May 1995) and PNNL Building America Solution Center — settled R/inch for blown cellulose (3.2–3.8) and attic fiberglass (2.2–2.7); DOE Energy Saver insulation-materials pages (2016 archive; the live pages have been retired) and InspectAPedia R-value table — batt and generic material ranges; Manufacturer datasheets: Owens Corning FOAMULAR 250 (XPS R-5.0/in per ASTM C578; lifetime warranty at 90% of labeled), ROCKWOOL ComfortBatt, Johns Manville Spider Plus (dense-pack R-15 @ 3.5 in), EPS-IA Type I data (≈3.85 @ 75 °F); PIMA performance bulletin (foil-faced polyiso 5.6–6.9/in LTTR), Building Science Corp. Info-502 and NRCA (Professional Roofing, 2016) — polyiso labels vs in-service 5.7/in; EPS-IA 2016 bulletin on XPS thermal drift