A filter cake is formed by the substances that are retained on a filter

Filter (chemistry)

In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...

. The filter cake grows in the course of filtration

Filtration

Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids by interposing a medium through which only the fluid can pass...

, 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. The specifications of the filter cake dictate the filtration method of choice