Technically, the barrels of all three types of pens are similar in design. The main difference lies in the inks used. For example, the gel pen has a gel-like ink that is thicker than the water-based ink of a rollerball, but thinner than the ink of ballpoint pens, resulting in different writing characteristics:
The rollerball, for example, is the pen with the most fluid ink flow in the literal sense, making it well-suited for particularly fast and gliding writing. The gel pen, on the other hand, feels very soft when writing and usually has the most intensive ink output. The ballpoint pen, on the other hand, impresses with the longest writing length and is usually the most durable of the three because the ink does not dry up even after a long time.
In principle, gel pens are suitable for anyone who likes to write softly and with intense colors. However, gel inks generally dry relatively slowly on the paper and small "ink lumps" can collect at the tip, which can make smudging a problem, especially for left-handers.
However, there are also gel pens for left-handers: the STABILO pointVisco gel pen, for example, has a special low-viscosity ink that dries particularly quickly.
Gel ballpoint pen is a synonymous term for gel pens. This is a technology that is similar in structure to a ballpoint pen, but offers a very soft writing feel. The reason for this is a gel-like ink, which on the one hand is more viscous than the water-based ink of a rollerball pen, but on the other hand is thinner than the ink of ballpoint pens.