Product Material: Non-woven, Active Charcoal cloth. 5 layers of PM2.5 filter ideal to protect your health. | Package: 20 x Replacement Protective Filter Pape | Note: This pm2.5 filter insert can not be cleaned and should be replaced every 1-2 weeks. When film or sticky sediment stains emerge, please replace the filter. | Used in combination to protect against dust, vehicle emissions, and smog. Ideal for cycling, running, biking, hiking, skiing and for other outdoor activities. | 跟卖，必送小红旗！！