A fountain pen is a nib pen that, unlike its predecessor the dip pen, contains an internal reservoir of water-based liquid ink. From the reservoir, the ink is drawn through a feed to the nib and then to the paper via a combination of gravity and capillary action. As a result, the typical fountain pen requires little or no pressure to write. Filling the reservoir with ink may be done manually, or via an internal filler mechanism which creates suction to transfer ink directly through the nib into the reservoir. Some pens employ removable reservoirs, in the form of pre-filled ink cartridges.