The uni-ball Air allows you to vary the width of your writing as though you were writing with a fountain pen without worrying about leaks. The unique technology means the ball is held within a plastic, not metal, surround allowing for more movement and greater pressure variations. This also makes for less friction when writing at an angle compared with other rollerballs. The more pressure applied when writing the wider the line you produce, the average line width variation is between 0.355mm and 0.55mm, allowing you to write freely with expression. Like many uni-ball products the Air comes with Super Ink which makes it permanent and secure, perfect for professional documentation.