The A1 filter belongs to the category of gas filters designed for respirators and half-masks. The letter „A“ specifies that it is designed for protection against organic gases and vapours with a boiling point higher than 65 °C. Such substances include, for example, solvents, thinners, paints based on organic solvents, or adhesives. The numeral „1“ indicates the filter's capacity, which in this case is the lowest in the series. This means it is suitable for work in environments with low concentrations of pollutants or for shorter working intervals. For easy recognition, this type of filter is standardly marked with a brown colour.