Spray Foam R Value Explained

R-value measures thermal resistance — how effectively an insulation material resists heat flow. Higher R-value means better insulation performance. Understanding R-value and how it relates to spray foam thickness is essential for estimating and quoting jobs accurately.

R-value per inch: Closed-cell spray foam: approximately R-6.0 to R-7.0 per inch, depending on product formulation Open-cell spray foam: approximately R-3.5 to R-4.0 per inch, depending on product formulation

Calculating R-value from thickness: R-value = thickness (inches) × R-value per inch

Example: 3" of closed-cell foam ≈ R-18 to R-21 Example: 5.5" of open-cell foam ≈ R-19 to R-22

Building code R-value requirements: R-value requirements for walls, roofs, and floors vary by climate zone (IECC climate zone 1–8). Higher climate zones (colder climates) require higher R-values. Always verify local code requirements for the specific application.

• Important notes on R-value:
• Aged R-value (long-term thermal resistance) is used for closed-cell foam. Blowing agent gas gradually diffuses from closed cells over time, slightly reducing R-value from initial values.
• Open-cell foam R-value does not change significantly over time as the open cell structure does not trap gas.
• R-value is a thermal measurement only. Spray foam also provides air sealing and moisture control benefits that R-value alone does not capture.