A Pleated Filter Cartridge has a very thin cross-section and retains oversized particles on the upstream side of the media. Pleated filters are particularly suited to removing rigid, irregularly shaped particles. These particles accumulate with time and form a 'cake' across the filter pores, but still allow flow through the filter. Descriptions of depth filters and pleated filters usually emphasize the extreme characteristics of each. In reality, the filtration process is somewhere on a scale between the two, leaning predominantly to one end or the other. Much of the pleated media used in cartridge filters has some depth characteristics aiding particle retention.