A spring and secondary sealing element in the dynamic part of rotating and stationary metal bellows seals (see also bellows mechanical seal). Rolled bellows are manufactured from thin-walled tubes (including longitudinally welded), into which the corrugations are spun either mechanically by means of a multiple roll process or hydraulically. The corrugations are produced one by one, i. e. the initial tube's material forming the corrugation can flow from the tube length without impairment of the bellows life due to thinning. Multiple walled bellows can also be used in mechanical seals if so dictated by the given pressure loading. Rolled bellows display a high spring rate and low hydraulic responsiveness, so they are employed in mechanical seals only when there is a definite demand for their specific merits (insensitivity to dirt, easy cleaning, thermostability). Cf. sterile operation, metallic expansion joints.