Safety Works Toxic Dust Filter Cartridge provides the highest level of dust protection with its P100 filters, which are by NIOSH (National Institute for Occupational Safety and Health). These cartridges are designed with an air flow opening positioned at the back, reducing the chance of dust and debris clogging the filters. This thoughtful design also allows for an easy fit check by blocking the cartridges with your thumb while wearing the respirator. Each package contains two cartridges in a convenient clamshell package, ensuring you have reliable protection when you need it. Model Number: SWX00324