Filter Insert : PM2.5 Face Mask Activated Carbon Filter Insert - New in sealed packages - 40 per pack - 72 individual packs - PM2.5 filter works by creating an electrostatic barrier that captures the microscopic particles that common mask fabrics like cotton and polyester can't effectively block on their own. $8/pack, 5 pack minimum purchase ** Please reference item #210513-2600-05 when contacting us about this listing. Return Policy Items are sold as-is as described and pictured. Most items come with a 7 day option to return and a 30 day limited parts warranty. Feel free to call before you buy. 888-649-6497