Kraftliner and kraft-top liner typically consists of two or more plies that are formed separately and combined by couching. The Z-strength tends to be limited by the ply adhesion, and the softwood kraft pulp used is commonly refined beyond the optimum for tensile strength to ensure sufficient Z-strength. In this work, two-ply forming by successive twin-wire roll forming, was evaluated with moderately refined never-dried unbleached softwood kraft pulp and recycled pulp in different plies. Successive twin-wire roll forming involved two-sided roll forming of the first ply and onesided roll forming of the second ply directly onto the first ply. Two-sided roll forming of the recycled pulp and onesided roll forming of the kraft pulp was evaluated in parallel to the reversed combination. The Z-strength was found to be limited by the strength of the kraft ply rather than by the ply adhesion. The effect on Z-strength when changing headbox consistency or when going from one-sided to two-sided roll forming for the kraft ply was in agreement with results for single-ply forming. Besides the favorable findings for Z-strength, the results suggest that successive roll forming enables an efficient utilization of the tensile strength potential of the softwood kraft pulp.