Quasi-molecular flux was the state of a solid material, like the metal in a starship's bulkhead, when it was passed through by spatially-inverted tetryon particles, creating a subspace particle stream. The structure of the material was thereby altered on a sub-atomic level.

The metal in the bulkhead in cargo bay 4 aboard the USS Enterprise-D was brought into quasi-molecular flux by the tampering of solanogen-based lifeforms who were attempting to form a spatial rupture in the cargo bay. (TNG: "Schisms")