A sheet forming tool (1) for the manufacture of a corrugated sheet has a lower tool element (40) and an upper tool element (50), each of the upper tool element and the lower tool element having a front side (23, 33, 41) and a rear side (25, 35, 42). The lower tool element (40) comprises a first base element (2, 4, 6, 8) and a first finger element (3, 5, 7, 9) projecting from said first base element (2, 4, 6, 8). The first finger element (3, 5, 7, 9) forms a first ridge (22, 24, 26, 28) for forming a corrugation peak in the sheet. The upper tool element (50) comprises a second base element (12, 14) and a second finger element (13, 15) projecting from said second base element (12, 14), the second finger element (13, 15) forming a second ridge (32, 34) for forming a corrugation trough in said sheet. The first ridge (22, 24, 26, 28) is arranged opposite to the second ridge (32, 34) and the first ridge (22, 24, 26, 28) is offset from the second ridge (32, 34) so as to allow for an engagement of the first finger element (3, 5, 7, 9) and the second finger element (13, 15) in an engaged position. Each of the first ridge (22, 24, 26, 28) and second ridge (32, 34) comprises a main portion (20) and an end portion (11, 21) and the angle ? (36) between each of the first ridge (22, 24, 26, 28) and second ridge (32, 34) in the main portion (20) and the corresponding front side (23, 33, 41) is at least partly different from the angle between each of the first ridge (22, 24, 26, 28) and second ridge (32, 34) in the end portion (11, 21) and the corresponding front side and a space is provided between the first finger element (3, 5, 7, 9) and the neighboring second finger element (13, 15) in the engaged position.