The air supplied to the clean room must have a very high degree of cleanliness. Therefore, it is necessary to choose an efficient or sub-efficient filter (for lower levels of cleanliness) as the terminal filter, which serves as the last level of filtration before the air enters the clean room. To protect the terminal filter and extend its lifespan, the air must first be filtered by a medium-efficiency filter. Depending on the clean room's classification, the flow pattern should be chosen carefully to avoid vortex zones in the working area.