Clean rooms control particles in the air by using HEPA or ULPA filters, using laminar (unidirectional) or turbulent (turbulent, non-unidirectional) airflow principles. Laminar or one-way air flow systems direct filtered air in a constant downward or horizontal direction to a filter located on a wall near the cleanroom floor, or recirculate through a raised perforated floor. Laminar air flow systems are typically used on 80% of clean room ceilings to maintain constant air. Stainless steel or other non-shedding materials are used to construct laminar air flow filters and hoods to prevent excess particles from entering the air.
Turbulent, or non-unidirectional, air flow uses laminar air flow hoods and non-specific velocity filters to keep the air in the clean room in constant motion, although not all in the same direction. Rough air tries to trap particles that may be in the air and drive them to the floor, where they enter the filter and leave the clean room environment.
Some places will also increase the vector clean room: air supply at the upper corner of the room, fan high efficiency filter is used, ordinary high efficiency filter can also be used with fan air supply outlet, and the return air outlet is set at the lower part of the other side. The height to length ratio of the room is generally between 0.5-1. This clean room can also achieve level 5 (100) cleanliness.