Are HEPA cabin air filters worth it, or do they hurt airflow?

This is the single biggest disagreement in the signals we read. Bosch's HEPA line is rated 99.97% at 0.3 microns and is praised across r/Acura, r/Subaru_Outback and other specialist subs for noticeably cleaner air. But the high-trust r/cars discussion and multiple subreddit threads (r/cmaxhybrid, r/SubaruAscent, r/AskMechanics) consistently report airflow drops on the order of 20–25% versus OEM, and at least one subreddit user flagged a concern about blower-motor stress. If allergies or smoke are your priority, HEPA wins; if maximum AC performance matters more, a quality activated-carbon paper filter is the safer call.