The bellow of a steel expansion joint can be made as both multi-layer (most common) and single-layer (less common).
The number of layers in a steel bellow depends on the parameters of the expansion joint, which include design pressure, temperature and value of design displacement.
The multi-layer bellows can have from 2 up to 10 layers.
The thickness of a single bellow layer is from 0.2 mm up to several millimetres.