Chizimi is a special polyester thread that sews like regular thread until it is exposed to steam. Then thread shrinks 30% to create shirring and gathers. Use in bobbin only for less puckering or use in both bobbin and as top thread for more puckering. Will work with any fabric, but works best with lightweight fabrics such as silk, chiffon, or organza. 330y (300m) spool.