Uni-Ball Gelroller One P Soda

The Uni-Ball Gelroller One P is the pocket-sized variant of the One – shorter, thicker, grippier. The "P" stands for Pocket: the compact plastic barrel with a maximum diameter of 14 mm sits securely in your hand, even when you're in a hurry. The ink color Soda is a muted, cool light blue – the barrel that rests in your hand, while black pigment ink with a 0.38 mm line width is applied precisely to paper.

Special Features

• Large-particle pigment ink remains on the paper surface: The specially developed uni-ball One ink contains larger pigment particles that don't penetrate the paper fibers but remain on the surface. The result: saturated, deep black – denser and more opaque than conventional gel ink. The ink is waterproof and archival.
• Quick-drying and sharp-edged: Because the liquid is quickly absorbed while the color particles remain on top, the line dries rapidly and doesn't feather. No smudging after writing.
• 0.38 mm line width: Fine, controlled lines – ideal for tight ruling, small handwriting, and detailed notes in confined spaces.
• Short, wide barrel in pocket format: 117 mm length with 14 mm maximum diameter. The compact body distributes grip pressure differently than a slim standard pen – less finger pressure needed, less fatigue during short writing sessions.
• Wire clip with wide opening: The sturdy metal clip can be spread wide and holds the pen securely on notebook covers, rings, or book covers – without damaging the binding.
• Refillable: Compatible with the gel refill UMR-38S (0.38 mm) from the uni-ball One series.

Application & Tips

• A6 and pocket notebooks: The compact length of 117 mm is proportional to small formats – the pen doesn't protrude beyond the book cover when inserted sideways.
• Thin paper: Because the pigment particles remain on the surface rather than soaking in, light paper (e.g., 52–68 g/m²) shows hardly any show-through. Even on Tomoe River paper, the One ink delivers a clear, sharp-edged line.
• On the 72g Tomoe River paper of the Hobonichi Techo, the One ink shows its best performance – no show-through, sharp line, quick-drying."
• Right-handers and left-handers: The quick drying time reduces smudging, which is particularly relevant for left-handers.
• Daily planners and to-do lists: For small, dense handwriting in calendars or bullet journals, 0.38 mm is a classic choice – the black ink stands out clearly even on colored pages.
• On the go: The clip holds on bag openings or notebook covers; the short barrel fits into any trouser pocket.

For Ink Technology Enthusiasts

The uni-ball One ink works with so-called BEADS-PACK pigments: dye molecules are enclosed in larger particle structures, which reduces their penetration depth into the paper fiber. The liquid portion of the ink is quickly absorbed while the color particles remain on top – this explains both the short drying time and the unusual color density. The jet black of the One line is measurably deeper than conventional black gel pens; Mitsubishi has also investigated memory effects in handwritten notes in collaboration with Ritsumeikan University. The ink is waterproof and pigment-based, but not solvent-based – it performs smoothly on smooth, calendered paper and shows hardly any bleeding on absorbent paper.

Technical Data