Ryco Microshield cabin air filters consist of 3 levels against proctection against biological contaminants. The biggest threat to safe breathing inside the vehicle can be 40 times smaller than the width of a human hair and invisible. The easiest way to protect a vehicle's passengers from airborne contaminants is Compatible With N99 MicroShield Cabin Air Filters by Ryco. Anti-bacterial agents within the media eliminate bacteria from the air flow and stops it growing in the filter N99 medical grade media layer with 99.7% efficiency @ 0.3 micron. Tested to ISO11155-2:2009 Captures miniscule particles that can penetrate deeper into the respiratory system Captures dust and dirt particles to keep the vehicle interior surfaces cleaner Protects vehicle occupants from harmful exhaust gases, noxious odours, soot and smog