This pen is worthy of being used either in the military or excursions to Antarctica. The pen writes in extreme conditions including wet surfaces, cool temperatures, and even upside down. Normal pens utilize gravity to create ink flow onto a paper. But the Uni-Ball Power Tank utilizes internal compressed air pressure to push out ink onto the paper. Revolving air inside allows it to continually push ink out until the end. The pen can write in weightless conditions such as in space, on wet paper and subzero environments. The oil based pigment ink is high density and comes out smooth and dark on paper. Pen also features a finely texturize grip composed of 0.16mm slits so that it not only fits comfortably in your hands but is also hard to slip away. Such a high-technology grip is only to be expected to match the high performance of this pen. Five body colors and red and blue ink refills are available.