🎾🪃🏹🪁 Bend-ability & Resistance 🪁🏹🪃🎾:

Paper grain also affects the property I call bendability (I don’t know if there is any established term): the ability of a sheet to be bent strongly without creating a crease. With good bendability, it is possible to perform many geometric constructions in origami without actually creating creases, or to make creases which abruptly end in the middle of the sheet. Such properties make it possible to cleanly fold tessellations and other models without making too many unnecessary helper creases. With bad bendability, even a slightly bent sheet will develop creases, and loose ends of creases in the middle of the sheet will not end cleanly, but creep on along the crease and to the sides, creating “crow’s feet”. The difference in bendability when folding along and perpendicular to machine direction may be huge, and creases may significantly differ in the way they look.

The difference in resistance when creasing along and perpendicular to the fibers affects paper shrinkage as well. Paper has a finite thickness. This means that a sheet folded in half is not exactly half as wide as the full sheet: a tiny bit of paper is used by the crease itself since the paper in the crease gets compressed and pushed aside, usually leading to a slight increase in thickness. The paper which creates the bulge has to be taken from somewhere and this leads to a shortening of the sheet in the direction perpendicular to the crease. This shortening will usually differ along machine direction and along cross direction. A single crease does not make a huge difference, but a grid consisting of dozens of lines can. Again, the thicker the paper, the stronger this effect usually is. This paper shrinkage may visibly affect the geometry of the folded model. For example, you may start from a very precise square, fold a dense grid with the same number of divisions in both directions, and find out that the sheet is not a square anymore. For a concrete reference point, when I folded the grid for Saturn Tessellation which was 128 grid divisions on a long-grain B1 sheet (longer edge of 100 cm), the sheet shrunk by about 2 cm along that direction, a difference clearly visible. Unfortunately, I didn’t measure the shrinkage along the shorter edge.

👌 Good Stuff 👌