These filters and cartridges are compatible with MSA Comfo Classic, Ultra-Twin, Ultra Elite Twin, and Duo-Twin reusable respirators. Particulate filters and vapor cartridges are NIOSH-rated and installed in reusable half-mask or full-face respirators to filter out airborne contaminants. They are selected based on the environment and type of respiratory hazards that need to be filtered. They can be changed out when they become dirty or when the type of contaminant changes. Filters and cartridges are compatible with a specific brand and mask model.