Just an idea for a printable piston I thought I'd jot down. It is designed to be printed without infill. The render is a cutaway, to show the bellows.

I *hope* this little thing extends downward as it is inflated from the top. Probably not much of a stroke until it is tuned properly.

I would like to use this thing to make a "pneumatic stepper motor" like my other thing:
thingiverse.com/thing:33853

Any feedback is welcome.