The Uni-ball One UMR gel ink refill features a special gel ink with large pigment particle, which means the ink will more likely to stay on the surface of the paper instead of blending through. This makes the colour of the ink looks brighter and more colourful on the paper. It also helps preventing smudges. It is also a fast-drying ink. Your writing will always look clear and crispy! It is produce for refilling the Uni-ball One Gel pens.