Method of treating a fiber cushion body

A fiber cushion body (1), which is formed from cross-linked fiber material and which is resiliently deformable when load is applied along a main load direction (2), is treated using ultrasonic energy. A portion (21) of the fiber cushion body (1) is displaced, for example using a sonotrode (20), and ultrasonic vibrations are applied to the fiber cushion body (1) to re-shape the fiber cushion body (1) from a first shape to a second shape different from the first shape.