Filter efficiency is only one element of filter performance. Capacity, restriction,
and service life should also be taken into consideration when evaluating a filter.
These other factors reflect the amount of dirt the filter can hold, how easily air
can flow through the filter, and how long the filter can be used before servicing. A
brick wall, for instance, would be likely to filter 100% of particulate matter—but
would of course provide very limited airflow! K&N filters are designed to strike a
desirable balance between efficiency, capacity, durability, and airflow.