This uni power tank 201 ballpoint pen features a pressurised ink delivery system meaning the pen will continue to write even when upside down or in extremely cold conditions. The ink is oil-based and will write smoothly without skipping if you are writing quickly. The nib has a size of 0.7 Mm. You can use it to write on paper, shiny surfaces, wet paper and even underwater. The ink is oil-based and comes out smooth and dark. It has a pocket clip so you can take it on the go with you. This is a heavy duty pen, making it ideal for on the go writers or anyone with an adventurous side.