These are bookbinder's linen (or actually it feels like plastic), with a line structure:
These are really thin papers, like tissue paper, painted with water-based inks. They're used for chirigi-e, a technique where you tear paper into shapes to combine the shapes into pictures.
The large sheets were 100x70 cm, and we had to make a folder to hold the sheets flat... But now they're much easier accessible than when we would store them in a cardboard tube!
Tomorrow we're going to St. Niklaas with ishtar, to a Bookbinder's trade fair -- but I don't think we'll be buying any paper there. ;)