A fountain pen comprises a hollow barrel such as can be held by a user, a nib stably attached to one end of the hollow barrel, also an ink cartridge housed internally of the hollow barrel and having a given containment volume. The cartridge is connected to the nib by way of a feed through which ink flows to the nib, and deformable by expanding at least partially between a normally undeformed first configuration, and a deformed second configuration in which the containment volume created internally is greater than the containment volume in the undeformed configuration.