An airtight seal over the headphone speakers and the ear stops background noise coming in and the music you're playing leaking out.

Or use it as an airtight seal for biscuits or crispbreads whose wrappings have been hastily torn.

It forms an airtight seal preventing microbiological and other contamination.

The capture ring aligns them, pulls them together and deploys 12 structural hooks, latching the two systems with an airtight seal.

Unfortunately, most furnace filters are slid in place without an airtight seal, which allows air to pass around the filters.