A seam joining together at least two web materials in an overlapped manner by ultrasonic welding, heat bonding or the like, in a bonding pattern (4) comprising a first bonding pattern (5) and at least one second bonding pattern (6) extending in longitudinal direction along and adjacent at least one side edge (1a, 2a) of the overlapped portion. The bonded area of the second bonding pattern (6) occupies more than 30 % of the combined bonded area of the first and second bonding patterns. The bonding elements (5a) of the first bonding pattern (5) have a mean area that is at least 2 times the mean area of the bonding elements (6a) of the second bonding pattern (6). The contact area of the bonding pattern (4), as seen in transverse direction of the seam, is between 10 and 30% of the width (w) of the bonding pattern (4) at any given point along the length of the bonding pattern.
