The TWSBI Eco Transparent Mint Blue Fountain Pen is made for the beginner who just wants to try out fountain pens, all the way to the experts. A good everyday worker. The pen cap is able to post onto the back of the pen. It's a piston-filler fountain pen. Simply dip into ink, screw back the end cap, and you're done! Ready to write!! Pen cap has an inner cap to insure a perfect seal when stored away.