I've packed my current Sketchnote travel set, consisting of a SketchOne and two FineOne from Neuland - one color, one gray for accents and shadows - in the box. Then I tried a MicronPigma Fineliner and two Pitt Artist Pens. Three pens definitely go and that's the Sketchnoters Mini-Set for on the way. A fourth pen has limited space. Contrary to the FineOne, the caps of the Pitt Artist have a clip - with a fourth pen, for example a Fineliner with a different line width, it will then be tight in the rolled material. Goes though.