R-value measures resistance to heat flow — higher is better. This chart gives the R-value per inch for common insulation types, so you can compare materials and hit a target.
| Material | R-value per inch |
|---|---|
| Fiberglass batt | 3.1 – 3.4 |
| Blown fiberglass | 2.2 – 2.7 |
| Blown cellulose | 3.2 – 3.8 |
| Open-cell spray foam | 3.5 – 3.6 |
| Closed-cell spray foam | 6.0 – 7.0 |
| Rigid EPS foam | 3.6 – 4.2 |
| Rigid XPS foam | 5.0 |
| Rigid polyiso | 5.6 – 6.5 |
| Mineral wool batt | 3.0 – 3.3 |
Total R = R-per-inch × thickness. For example, 6 in of fiberglass batt gives roughly R-19. Cold-climate attics are often insulated to R-49 through R-60.
FAQ
Is a higher R-value always better for insulation? Generally more R-value means better insulating performance, but it comes with diminishing returns and higher cost as you go up, and the ideal R-value for a given wall, ceiling, or floor is set by climate zone and code minimums rather than simply maximizing R-value.
See the How to Install Insulation guide.