The pen is closely related to the ballpoint pen. The difference between these lies in the ink and writing experience. A rollerball pen has a water-based ink, not oil-based, as in a traditional ballpoint pen. The water-based ink flows freer from the tip and goes deeper into the paper, which also makes the pen feel soft and comfortable to use. Rollerball is the perfect pen for those who want a little more fluid feeling when writing or sketching!