You might have seen a bamboo mat — for making sushi rolls. These mats are called "Su (簀)" in Japanese and you should see the ones for papermaking — Hiki-Su is unbelievably fine and delicate.
Su for paper making is called Hiki-Su
Because bamboo has nodes that make bumps, artisans of Hiki-Su use only the culm section (the parts between the nodes) which are limited in length. They carefully join each hyper-thin strip with silk string to make a larger, smoother Hiki-Su that doesn't fall apart after years of the papermaking process.
The bamboo rods are not actually joined, they are lined up end-to-end with silk string.
Only highly skilled artisans can make Hiki-Su, (also, the silk string has specifically been made for Hiki-Su!) and very few of them are available today.
Su placed in a frame called Keta in sheet forming process
Paper in the image: CON1451 Kobayashi Kadoide Light, 24g, 25x37" (Heritage Washi)
If you want to know if the washi is high-quality and handmade, look at the surface carefully. The thin marks of Hiki-Su are one of the easiest signs and you will feel the breathtaking work of the artisans who made them.