In the ink jet printing technology, two types of mechanism were used traditionally in the ink jet cartridge market; the mechanical element and the sponge ink jet cartridge.In this paper we introduce a new type of pressure regulator in the ink jet cartridge. A bundle of fiber is bundled within a polyethylene film, and inserted into the ink tank of the cartridge. The matrix of the fiber in the fiber bundle is long and straight pipe like structure. The fiber is a good pressure regulator as it provides capillary force to suck the ink and to hold the ink under certain pressure environment The compactness of the fiber determines the capillary force and the amount of ink that the cartridge can hold it is important to the cartridge designer.It is found that, the fiber density influences the amount of the residue ink left in the cartridge after depletion, the ink usage efficiency of the ink jet cartridge, and the yield of the ink cartridge. It is suggested to design the fiber density to within the critical fiber density limitation.