I have a couple of TWSBI Go pens, and one I completely forgot about. I left it inked for at least a year and a half...maybe a bit more. I found it the day before yesterday while looking for something else. I uncapped it and it wrote perfectly from the first stroke. I don't know about you, but that is pretty amazing to me. That inner cap fits over the nib and feed in an air tight seal, keeping every thing wet.