Rigid foam board R-value by thickness (EPS/XPS/polyiso)
Typical published planning values — NOT a certified design. Real performance depends on installation quality, framing / thermal bridging, moisture and settling; follow the product data sheet and your local energy code. Foam ignition/thermal-barrier, vapor/moisture control and combustion-air safety are set by the manufacturer and code — check with a professional.
Rigid foam board delivers R = thickness × R/inch, and R/inch differs by foam type. The table below shows labeled R by thickness for EPS, XPS and polyiso at their band midpoints — confirm the rated R on the board; polyiso drops in the cold. Use it with the rigid-foam board calculator and the rigid-foam R & sheet calculator.
| Thickness | EPS | XPS | Polyiso |
|---|---|---|---|
| 1.0" | R-3.9 | R-4.75 | R-6.05 |
| 1.5" | R-5.85 | R-7.13 | R-9.08 |
| 2.0" | R-7.8 | R-9.5 | R-12.1 |
| 3.0" | R-11.7 | R-14.25 | R-18.15 |
Labeled R by thickness at the band midpoint (EPS ~3.9, XPS ~4.75, polyiso ~6.05 R/inch). Confirm the rated R on the board — polyiso’s R/inch drops in cold temperatures.