A fu is brushed onto yellow paper in cinnabar or vermillion ink, using a script that deliberately is not ordinary written Chinese, a stylized talismanic form, fu wen, built from character elements combined in ways no reader would encounter in a newspaper or a letter.
Why the writer matters as much as the paper
Practitioners hold that an effective fu depends on who writes it and under what conditions, an ordained Daoist priest, daoshi, produces one after specific purification, in a single continuous ritual motion while maintaining a particular internal state, rather than any person copying the visual pattern from a book. A fu produced without that ritual standing is generally regarded within the tradition as inert regardless of how closely it resembles a proper one, which is why mass printed reproductions sold as souvenirs are not considered equivalent to a priest made talisman.
How it is used, and what happens afterward
A fu is used in several ways depending on its purpose, posted on a door, carried on the person, or in some practices burned and the ash mixed into water or tea to be consumed. Once its purpose has run its course, a fu is commonly burned rather than kept indefinitely or thrown away with ordinary paper waste, treating its disposal as part of completing the working rather than an afterthought.