Wiktionary
airtightness
n. The quality of being airtight.
Usage examples of "airtightness".
Byron heard the old hiss and sigh, as though the boat were a live monster taking a deep breath, and felt in his ears the sudden airtightness, before the chief below called, "Pressure in the boat!
The process returned the flagship to proper airtightness so long as she remained at rest.