Filter cake

A filter cake is formed by the substances that are retained on a filter. 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 viscosity of the filter cake gets too high, thus too little of the mixture to be filtered can pass through the filter cake and the filter plugs. The specifications of the filter cake dictate the filtration method of choice

...
Wikipedia