Editing Filter paper (section)

===Air filters===
[[File:Air filter, opel astra(2).JPG|thumb|Air filter paper in an auto engine]]
{{Main|Air filter}}
The main application for air filters are [[combustion air]] to [[engine]]s. The filter papers are transformed into filter cartridges, which then is fitted to a holder. The construction of the cartridges mostly requires that the paper is stiff enough to be self-supporting. A paper for air filters needs to be very porous and have a weight of 100–200 g/m<sup>2</sup>. Normally particularly long fibrous pulp that is mercerised is used to get these properties. The paper is normally impregnated to improve the resistance to [[moisture]].<ref name="Paulapuro_2000"/>{{rp|page=113}} Some heavy duty qualities are made to be rinsed and thereby extend the life of the filter.