Oil-based ink, expelled from the pen by air compressed to 3000hectopascal to ensure smooth writing performance and a distinct line quality. Pressure forces ink out of the pen, ensuring uninterrupted ink flow even when you are writing quickly. There are no spots or broken lines. Even if you only press lightly, you can achieve smooth and even lines. Another feature of uni POWER TANK is Longer Shelf Life. The compressed nitrogen gas in the ink cartridge allows the ink to remain fresher for longer. Writes smoothly on the wall calenders, and flipcharts. Even when the pen is held in an upward position there is no ink back-flow and the pen continues to write smoothly. This is an all-weather pen that can be used in any environment, including outer space.