On roughness such as ones consisting of a protuberance, junctions and small steps, the loss of adhesion is noticeable. However, compared to previous comparable devices [5], a distributed system has the advantage that the loss of adhesion tends to be less critical. A protuberance or step in the middle of the pad might prevent effective contact of a considerable area of the pad (with the consequent proportional loss of adhesion), but in a non-compliant nondistributed system the loss tends to be more drastic. Because the adhesion is distributed the system is more robust.