5N11 Particulate Respirator FilterHow I use these: The 5N11 Respirator Filter Cotton is designed to be paired with the 6001 Filter Cartridge and attached to the outside with a particulate filter cap. This product can be found in my product list, and is effective at capturing large particulate matter to extend the lifespan of your 6001 Cartridges, which can be quite costly. Replace the 5N11 when airflow restriction is noticeable while using your mask. Description: 50PCS 5N11 Respirator