pack comes in different sizes: 0.05, 0.1, 0.2, 0.3, 0.5,
Ink: The ink is jet black and yes it's waterproof on regular paper. I haven't tried it on cold-pressed watercolor paper yet. Can't imagine there would be an issue though.
The lines made by the pens are straight, clean and even in size. I don't get globs of ink at the beginning or end of a line like with some other gel pens.