Moldex cartridges snap-into the facepiece eliminating the chance of misthreading and misaligning. New inhalation valve comes on each cartridge eliminating need to replace. Organic Vapor Cartridges are NIOSH Approved for Organic Vapors. Acid Gas Cartridges are NIOSH Approved for Chlorine, Hydrogen Chloride, Sulfur Dioxide, Chlorine Dioxide, Hydrogen Fluoride or for escape only from Hydrogen Sulfide. Organic Vapor / Acid Gas Cartridges are NIOSH Approved for Organic Vapors, Chlorine, Hydrogen Chloride, Sulfur Dioxide or Chlorine Dioxide, or for escape only from Hydrogen Sulfide; or Hydrogen Fluoride. Ammonia / Methylamine Cartridges are NIOSH Approved for Ammonia and Methylamine. Formaldehyde Cartridges are NIOSH Approved for Formaldehyde. Multi-Gas / Vapor Smart® Cartridges are NIOSH approved for Organic Vapors, Ammonia, Methylamine, Chlorine, Hydrogen Chloride, Sulfur Dioxide, Chlorine Dioxide, Hydrogen Fluoride, Formaldehyde and Hydrogen Sulfide (escape only). P100 Particulate Cartridge Certified under NIOSH 42 CFR 84 to have a filter efficiency level of 99.97% or greater against oil and non-oil based particulate aerosols. Cartidges and filters are sold 2 per pack.