The Uniball One P is a portable mini version of the popular Uniball One gel pen. It is shorter and fatter than the original Uniball One. Each pen comes with the dark "Uni-ball One" ink formula with a muted-coloured barrel. The newly-developed "Uni-ball One" ink minimizes the penetration of the ink into the paper fibre. As a result, it develops original colours on paper, showing a darker black than an ordinary black ink pen, and showing more vivid colours than other coloured ink pens. The series of Uni-ball One P gel pens are available in 5 barrel colours in 0.38 mm and another 3 barrel colours in 0.5 mm.