Rollerball pens were originally developed to combine the convenience of ballpoint pens with the smooth "wet ink" effect of fountain pens. Though like ballpoint pens they have ballpoint writing mechanisms, rollerbal pens make use of water-based liquid or gelled ink. The specificity of this less viscid ink, which tends to saturate more widely and more deeply into the paper, make rollerball pens unique in terms of writing qualities.

 

The use of this type of inks has both advantages and disadvantages. First of all, less pressure is needed to be applied to the pen to have it write cleanly. Second of all, the inks are usually more brightly and variously colored, due to the wider choice of suitable water-soluble dyes, or to the use of pigments. As for disadvantages: the ink is more liable to smudge because water-based ink dries more slowly; also the ink may seep through the paper. In addition, rollerball pens usually do not last as long a standard ballpoint pen because the liquid water-based ink is dispensed at a much quicker rate. They are also more likely to leak ink in case when the cap is not put back on (in the pocket, bag, etc.).

All in all there are two types of rollerball pens: those that use a liquid ink and those that use a gelled ink.

With liquid ink rollerball pens the ink is often thin enough that it will soak through or, how they say, ‘bleed’ through the entire paper, what makes the second side of the paper totally unsuitable for writing or unreadable if still written on. Gelled rollerball pens use a jelly-like ink: when writing the ink thins as it moves past the ball and sets back up just after it is applied to the paper. Because the gel inks set so quickly, they do not sink into paper fibers as much as liquid ink. Thus, one may write on both sides of the same piece of paper.

Various rollerball pens can be a nice contribution to every pens collection.