It is defined as an assembly that utilizes a fabric belt element to allow for the movement of ductwork, as opposed to a metal expansion joint which allows for the movement by means of convoluted metal bellows.
![Small diameter fabric expansion joint](https://usbellows.com/wp-content/uploads/2019/06/fabric-expansion-joint-17-300x225.jpg)
It is defined as an assembly that utilizes a fabric belt element to allow for the movement of ductwork, as opposed to a metal expansion joint which allows for the movement by means of convoluted metal bellows.