Common sense says the smaller the micron size you are trying to filter the more restrictive the airflow is going to be regardless of brand come on guys if the air flow even slightly restricted then no actual filtering is going on with in reason

These filters work fit just fine in my application air intake on my furnace and they filter out any particle down to a certain micron size mirv 12 is down to 3 microns

The fact that they are slightly less expensive makes it less painful to change the filters frequently