Roller ball pens are pens which use ball point writing mechanisms with water-based liquid or gelled ink, as opposed to the oil-based viscous inks found in ballpoint pens. The characteristics of these less viscous inks, which tend to saturate more deeply and more widely into the paper than other types of ink, give roller ball pens their distinctive writing qualities.
The roller ball pen was initially designed to combine the convenience of a ballpoint with the smooth "wet ink" effect of a fountain pen.
