Coalescing filters function in a different way from general-purpose filters. Air flows from inside to outside through a coalescing media. Coalescing by definition means "to come together." It is a continuous process by which small aerosols come in contact with the fibers in the filter media, uniting with other collected aerosols and growing to emerge as a droplet on the downstream surface of the media and then gravitationally drained away. For maximum performance and efficiency, coalescing filters should be preceded by a general-purpose filter.