Uni-ball Air UB-188L Red The Uni-ball Air allows you to vary the width of your writing. It’s like writing with a fountain pen without worrying about leaks. The unique technology means the ball is held within a plastic, not metal, surround. This allows for more movement and greater pressure variations. It 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 but with heavy pressure can reach almost 1mm The Uni-ball Air comes with Uni Super Ink making it waterproof, lightfast, permanent and secure, perfect for professional documentation.