PM2.5 Filter is designed to filter airborne particles that is less than 2.5 microns. It's composed of 5 different layers of activated carbon and fabrics with types of fibres including two layers of spun bound polyester for the interior and exterior side which is used to filter out larger particles, followed by a layer of activated carbon used to trap particulate matter, and two middle layers of high efficiency melt blown nonwoven polypropylene which is used to filter out small particles. Each order comes with ten(10) PM2.5 Filters.