HEPA filters are composed of a complex fiber system. Typically, fiberglass fibers with a diameter of 0.5 to 2 microns are used. The main factors influencing performance are fiber diameter and filter thickness. The air space between the fibers of a HEPA filter is significantly larger than 0.3 microns.
The idea that a filter acts as a sieve, allowing particles smaller than the largest openings to pass through, is incorrect for HEPA filters. While this sieve effect is also true for HEPA filters, it has a negative impact, leading to premature clogging, reduced filtration rate, and even filter failure. Although this effect is extremely undesirable, it is virtually impossible to eliminate.
