A filter cake
is formed by the substances that are retained in or on a filter
(depending on whether a depth or a surface filter is used). The filter cake grows in the course of filtration
, becomes "thicker" as particulate matter is being retained. With increasing layer thickness the flow resistance of the filter cake increases. After a certain time of use the filter cake has to be removed from the filter, e.g. by backflushing. If this is not accomplished, the filtration is disrupted because the flow resistance of the filter cake gets too high, thus too little of the mixture to be filtered can pass the filter cake and the filter plugs.