UNIDIRECTIONAL AIRFLOW:- In a unidirectional airflow system, air is uniformly introduced through HEPA filters from one entire surface of the room, such as the ceiling or a wall. For unidirectional airflow, the filter coverage must be at least 80% coverage. The air flows perpendicularly from this surface at a constant velocity and is removed at the opposite surface (wall or floor). Unidirectional flow provides a direct, predictable path that a sub-micrometer size particle will follow through the cleanroom, with the minimum opportunity for contaminating room components. It also captures the particles constantly generated within the room and introduced into the airstream, thereby reducing the potential for cross-contamination.

NON-UNIDIRECTIONAL AIRFLOW:- In a non-unidirectional airflow system, air is supplied to the cleanroom conventionally through HEPA filters in a random airflow pattern and mixes with internal air by induction.

MIXED AIRFLOW:- A mixed airflow system may be used in a cleanroom with two (or more) areas requiring different classifications. Non-unidirectional airflow and unidirectional airflow will sometimes exist in the same space and may be classified independently.