This is a high performance HEPA type filter -- not unlike the types we see now on vacuum cleaners. The purpose of this part is to remove dust and airborne particles before they get into the car through the ducts. This is good, but the filter adds some drag to the system - and as a result the A/C and defrost system may be slightly less effective with the filter installed. It should be replaced every 7.5k miles -- which adds to maintenance cost. These are the tradeoffs.