What kind of cord is the 'Sanadahimo' mentioned in the congratulatory money envelope description?

It is not a round twisted thread, but a flat woven fabric. The knot cords used for typical celebratory envelopes are made into a round shape by twisting several strands of thread. On the other hand, syubisya PRINTING lab's congratulatory money envelopes use Sanadahimo, woven by crossing horizontal and vertical threads flatly^[1][2].

It is tough. Sanadahimo is a traditional cord that does not stretch or break easily, to the extent that it was used to bind armor, weapons, or heavy luggage. Because it is woven like cloth rather than twisted, it firmly withstands pulling forces. Added to this is fukuro-ori, a tubular weaving method that leaves the inside hollow like a tube, making it feel smooth to the touch without prominent seams on the edges^[3][4]. Thanks to its flat surface, it adheres closely to the envelope's exterior without lifting, and with moderate friction, knots once tied do not easily slip loose.

hmmm, the tough woven cord laid over the thin paper envelope reads as neat thoughtfulness wishing that the knot will not loosen while delivering congratulations.