HERE ANOTHER ONE VIA SPYING, LEAVE OUT ALL THE REST
Any filter that will catch a virus - has openings in the filter too small to permit reasonable airflow.
A virus is an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. They range in size from about 20 to 400 nanometres in diameter (1 nanometre = 10-9 meters). By contrast, the smallest bacteria are about 400 nanometres in size.
If you can design, produce, and market such a filter - that effectively catches viruses yet permits adequate air flow - You can retire.
Originally Posted by oeb11