The ability of a package to prevent exchange of its internal gas with the external atmosphere. The figure of merit is the gaseous leak rate of the package measured in Pa-m -sec .

The measure of a connector's permeability to gas ingress. In general terms it means how "airtight" the device is when measured in air-leakage tests. Since all materials are ultimately permeable to gas ingress at some point, hermeticity ratings are used to define acceptable performance levels as required by each individual application.

The extent to which a seal is hermetic.