If it is a volatile substance that adheres, it may subsequently evaporate from the aerosol filter. Consequently, it is important to design a filter whereby the gas filter component is located after the aerosol filter. The gas filter component of the protective filter consists of active carbon. Recently other adsorbants, e.g., different synthetic polymers and zeolites have been tested but none has proved as widely applicable as active carbon. Neither have any other absorbents been found to have higher uptake ability for CW agents than active carbon.
Active carbon is produced by heat-treating different organic materials.
A number of commonly-used materials are peat, coconut shell and coal. The carbon so obtained contains numerous pores and cavities and under magnification looks rather like a face sponge. By selecting different starting materials and conducting the activation in different ways, the active carbon obtained has different degrees of pore distribution. Carbon with large pores is the most suitable for cleaning water, whereas carbon with small pores is better for removing gas. Pore distribution and pore size are also important for the carbon's ability to absorb water.