Pm2.5 Filters: 80s-yellow (moderate Pollution) 90s-orange (high Pollution) 95s-red (severe Pollution) 99s-purple (hazardous Pollution) one Pack Contains 5 Pairs Of Filters. We Recommend You Change Filters Every 2 Weeks. Also Change Them If They Get Wet, Look Very Dirty Or Are Hard To Breathe Through. our 80s, 90s, 95s And 99s Filters Include A Medical Grade Nano-silver Coating That Kills Bacteria And Viruses. All Our Filter Protect Against Particulate Matter (pm). use The Air Quality Index (aqi) To Choose Filters: Use The Airvisual App Or The Waqi Website To Check The Air Pollution (aqi) In Your Area Or City choose A Filter That Matches The Color Of The Aqi. For Example, If The Aqi Is Orange, Choose The 90s-orange Filters higher Filters Are Harder To Breathe Through And Also More Expensive, So Dont Choose A Higher Level Than You Need all Filters Are Tested At Nelson Labs, Usa In Compliance With Us-fda Regulations 21 Cfr Parts 210, 211 And 280 At A Particle Size Down To 0.1 Microns. Blocks Up To 99% Small Airborne Pollution (pm2.5).