One inch of EPS foam board is about R-3.9 at 10 and 13 psi, R-4.2 at 15 psi, and R-4.4 to R-4.5 at 25, 40 and 60 psi, at 75°F mean temperature.
EPS Foam Board R-Value & Thickness Guide
How much R-value does EPS foam board give you?
EPS foam board gives about R-3.9 to R-4.5 per inch at 75°F, depending on its density and compressive strength. Denser, stronger board has a slightly higher R-value per inch. The charts below show the R-value of EPS at each thickness, and how thick the board needs to be to reach R-5, R-7.5, R-10 and R-15.
Need more than R-15? Stack layers, or ask us for thicker custom cuts. Insulfoam notes that EPS can be made up to 40 inches thick, compared with about 4 inches for XPS. Ready to price a job? Request a quote, or see our EPS foam sheets and boards.
Three Rules of Thumb
Plan on about R-4 per inch
Most EPS board lands between R-3.9 and R-4.5 per inch. Higher-strength board is a little higher.
Check the test temperature
R-values are published at a mean temperature, 75°F in most charts. EPS tests higher at colder temperatures.
Stack layers for more R
For high R-values, use more than one layer and stagger the joints, or order thicker custom cuts.
EPS R-Value Charts
R-value per inch by compressive strength, and total R-value by thickness. All values are typical, at 75°F mean temperature.
R-value of EPS foam board by thickness and psi
| Thickness | 10 psi | 13 psi | 15 psi | 25 psi | 40 psi | 60 psi |
|---|---|---|---|---|---|---|
| 1/2 in | 2.0 | 2.0 | 2.1 | 2.2 | 2.2 | 2.3 |
| 3/4 in | 2.9 | 2.9 | 3.2 | 3.3 | 3.3 | 3.4 |
| 1 in | 3.9 | 3.9 | 4.2 | 4.4 | 4.4 | 4.5 |
| 1-3/16 in | 4.6 | 4.6 | 5.0 | 5.2 | 5.2 | 5.3 |
| 1-5/16 in | 5.1 | 5.1 | 5.5 | 5.8 | 5.8 | 5.9 |
| 1-1/2 in | 5.9 | 5.9 | 6.3 | 6.6 | 6.6 | 6.8 |
| 2 in | 7.8 | 7.8 | 8.4 | 8.8 | 8.8 | 9.0 |
| 2-3/16 in | 8.5 | 8.5 | 9.2 | 9.6 | 9.6 | 9.8 |
| 2-5/16 in | 9.0 | 9.0 | 9.7 | 10.2 | 10.2 | 10.4 |
| 2-3/8 in | 9.3 | 9.3 | 10.0 | 10.5 | 10.5 | 10.7 |
| 2-1/2 in | 9.8 | 9.8 | 10.5 | 11.0 | 11.0 | 11.3 |
| 2-9/16 in | 10.0 | 10.0 | 10.8 | 11.3 | 11.3 | 11.5 |
| 3 in | 11.7 | 11.7 | 12.6 | 13.2 | 13.2 | 13.5 |
| 3-9/16 in | 13.9 | 13.9 | 15.0 | 15.7 | 15.7 | 16.0 |
| 4 in | 15.6 | 15.6 | 16.8 | 17.6 | 17.6 | 18.0 |
Thickness needed for a target R-value
| Target R-value | 10 psi | 13 psi | 15 psi | 25 psi | 40 psi | 60 psi |
|---|---|---|---|---|---|---|
| R-5 | 1-5/16 in | 1-5/16 in | 1-3/16 in | 1-3/16 in | 1-3/16 in | 1-3/16 in |
| R-7.5 | 2 in | 2 in | 2 in | 2 in | 2 in | 2 in |
| R-10 | 2-9/16 in | 2-9/16 in | 2-3/8 in | 2-5/16 in | 2-5/16 in | 2-5/16 in |
| R-15 | 4 in | 4 in | 3-9/16 in | 3-9/16 in | 3-9/16 in | 3-9/16 in |
Plain EPS by ASTM C578 type: R-value per inch at three temperatures
| Mean temperature | Type I | Type VIII | Type II | Type IX |
|---|---|---|---|---|
| 25°F | 4.35 | 4.54 | 4.76 | 5.00 |
| 40°F | 4.17 | 4.25 | 4.55 | 4.76 |
| 75°F | 3.85 | 3.92 | 4.17 | 4.35 |
Sources: Atlas ThermalStar thickness selector and Cellofoam EPS typical physical properties. Download the R-value and thickness selector and the EPS typical physical properties sheet. Typical values, not a specification.
R-Value and Thickness Questions
What is the R-value of 1 inch foam board?
What is the R-value of 2 inch foam board?
Two inches of EPS is about R-7.8 at 10 and 13 psi, R-8.4 at 15 psi, R-8.8 at 25 and 40 psi, and R-9.0 at 60 psi.
How thick is rigid insulation for R-10?
About 2-5/16 inches of 25 to 60 psi EPS, 2-3/8 inches of 15 psi EPS, or 2-9/16 inches of 10 or 13 psi EPS.
How thick does foam board need to be for R-15?
About 3-9/16 inches for 15 to 60 psi EPS, and 4 inches for 10 or 13 psi EPS.
How thick is foam board?
EPS board is commonly cut from 1/2 inch up to 4 inches and thicker, in 4 × 8 foot sheets. Insulfoam R-Tech sheets run from 3/8 to 5 inches in 1/8 inch steps, and custom sizes and densities are available. Tell us what you need on the quote page.
How does EPS R-value compare with XPS and polyiso?
EPS has a lower R-value per inch than polyiso (about R-5.7 per inch for flat roof boards) and XPS (R-4.6 to R-5.0 per inch, per Insulfoam's comparison sheet). EPS costs less for the same R-value and keeps its R-value over time. See the EPS vs. XPS vs. polyiso guide.
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