Yes, I’m aware that companies sell HEPA cabin air filters for vehicles. But, is it safe to install a HEPA cabin air filter on a vehicle who’s HVAC system wasn’t designed for HEPA air filters?

https://www.engineersedge.com/filtration/hepa_filter_pressure_drop_considerations.htm

By design, HEPA air filters will create resistance to flow, and a high differential pressure drop will exist across the filter. Most HEPA air filter manufacturers literature suggests replacement of HEPA air filters when the resistance due to dust loading has reached 2 in.wg.

So if your car’s HVAC is designed for high airflow and you slap a HEPA filter on it, are you adding more stress and wear on the system? Seems like it’s the exact same problem of installing an overly restrictive filter on your home’s HVAC return vent.