The Uni PowerTank features a clever pressurised refill which allows it to write in extreme conditions: on wet paper; horizontally or even upside-down; in temperatures as low as -20°C; and, most importantly, in the zero-gravity of outer space! (Hey, you never know...). PowerTank works just like the more expensive Fisher Space pen, except the refill is transparent so you can see how much ink is left. Now the important bit: the world's first transparent pressurised refill works with compressed air at 3000hPa and employs a 'high gas barrier resin'. Got that? Good. Oh, and it's ludicrously cheap compared to traditional 'space pens'.