10 Filters in a Pack. PM2.5 is defined as "Particulate Matter that are 2.5 microns small" which tells you the size of the particles blocked completely by the filter. The coronavirus lipid is technically smaller than this, research tests show PM2.5 filters with a cloth mask will reduce airborne particulates by 90%. The PM2.5 filters are made with Five layers of protection:

• 10 Filters : Each Filter is recommended for about 24 hours of use (about a week of occasional use). 
• Size: 4.7in*3.23in (12cm*8.2cm)