The thermal resistance (R-value) of closed-cell foam insulation after the blowing agents have off-gassed and ambient air has diffused into the cellular structure. Because fresh foam traps high-resistance gases that slowly escape over years, the aged value provides a realistic measure of the building's long-term energy performance.
Heard on the job
The spec calls for an aged R-value of 21, so a standard two-inch application of spray foam won't pass inspection.
Also heard as
- long-term thermal resistance
- LTTR