The ink reservoir is a source which provides backpressure in an open-type ink cartridge. The properties of ink reservoir cause tremendous effects on the printing quality of whole inkjet system. It keeps the ink from leaking due to the natural gravity in the non-printing stage. As well as it supplies stable ink output in the printing stage.In this paper, the property and availability of reservoir material are studied. In particular, the completed processes in design, manufacturing and test of the reservoir for a commercial cartridge are explained. Furthermore, the backpressure mechanism is derived theoretically and experimentally. A backpressure experiment system is introduced here to present the interaction between the ink and the reservoir. The measurement and analysis are not only applied to sponge reservoir material but also fiber reservoir material.In addition, this paper suggests the issues about reservoir that cartridge manufacturers need to take care during the assembly and the delivery. The changes of external environment also influence the reservoir and may cause the cartridge malfunction. A good reservoir preparation can reduce the negative effects and raise robustness of a cartridge.