The problem with carrying ink is not the lid; it is the air. A half-full bottle in a bag goes through pressure and temperature changes and pushes ink past any seal. This well solves it with an internal silicone baffle that collapses as the level drops, so the air space above the ink stays near zero from full to empty.
The body is nickel-plated brass, 48 mm tall, 30 ml capacity, with a bayonet lid that locks in a quarter turn against a silicone O-ring. There is a machined internal shoulder that lets a converter draw the last 3 ml at an angle. It weighs 130 g empty.
We have carried one filled in a coat pocket for a fortnight, including two flights, with no leak. That is not a guarantee, and we would still not put it loose in a bag with a laptop. Dismantle and wash the baffle every few refills; ink dries behind it and it will stop collapsing cleanly.
