open film

Also contains definitions of: closed film, partly open film

A film in which mass transfer can occur between the film and the coexisting bulk phases, for all the components. The term partly open film applies to a film in which mass transfer can occur only for certain components. The term closed film applies to those films with fixed mass.
Source:
PAC, 1994, 66, 1667 (Thin films including layers: terminology in relation to their preparation and characterization (IUPAC Recommendations 1994)) on page 1671