Filters are classified by means of a letter and a color code. Chemical products can consist of: solids/particles (dust, fibers, microorganisms), or volatile substances (gases and vapors). Through the color and letter coding you can deduce which filter you need for the (chemical) substance you are dealing with.
| Type filter | Color | Protect against |
| A | Brown | Organic vapors and solvents with a boiling point >65° C |
| AX | Brown | Organic vapors and solvents with a boiling point <65° C |
| B | Grey | Inorganic acid gases and vapours such as chlorine (CL2), hydrogen sulphide (H2S) and hydrogen cyanide (HCN) |
| E | Yellow | Sulphur dioxide, hydrogen chloride(hydrochloric acid) |
| K | Green | Ammonia |
| HG | Red | Mercury fumes |
| NO | Blue | Nitrous fumes and nitrogen dioxide |
| CO | Anthracite | Carbon monoxide |
| I | Orange | Radioactive iodine and compounds |