airtightness; hermeticity
Technical term used in engineering, construction, and product design to describe the degree to which a container, seal, or structure prevents air leakage.
This container has high airtightness, so food stays fresh longer.
A test was conducted to measure the building's airtightness.
Compound of 気密 (airtight) + 性 (property, -ness). The word is a modern technical coinage.