The refillable notebooks are designed to accompany the Traveler's Notebook leather cover.
It can be incorporated inside of the Traveler's Notebook's using the rubber band that comes with the leather cover and you can also accommodate a couple of the refillable in the Traveler’s Notebook.
The refill notebook is made in Japan with Midori's original paper with the highest writing quality. It takes fountain pen ink well, with some show through but no feathering or bleed.
For those of you who like details, each page has 32 lines. The ruling space is 6.5mm (i.e. the lines are 6.5mm apart).
Midori in Japan