I cannot vouch for what the Japanese or the French words on the product label actually mean, but the Chinese words promise that the notebook is "show-through resistant". For the asking price, I was willing to give it a go and test its marketing claim, even though every set of five notebooks was wrapped in cellophane and I could not inspect or feel the paper therein.
This is how the reverse side of the page looked, after I've written quite densely on two-thirds of the front, using a variety of fountain pens and inks (of which the details are shown in the image at the bottom):
I then used the same pens and inks to write on the reverse side, so that there is a significant area of overlap in which there is writing on both sides, with the same pen and ink for each four-line panel:
in order to see how noticeable or distracting the level of show-through is:
My conclusion is that the resistance to show-through and/or bleed-through is less effective than what I think one could reasonably expect, in the face of the product's marketing claim. For the price I suppose these notebooks aren't that bad for use with fountain pens, although I know Muji could do better, because a different notebook (made in Japan) I bought on the same visit proved to be incredibly fountain pen friendly, and very resistant to feathering, show-through and bleed-through.
With these made-in-Indonesia notebooks, there is some woolliness observed when writing with certain inks, but no significant feathering. People who don't like the feel of the coating on bright white Clairefontaine paper (such as in the 'Age Bag' notebooks) probably won't like this paper either.
Edited by A Smug Dill, 09 May 2019 - 12:52.