With pure titanium that has about half the specific gravity of soft iron built into the head, the weight is distributed around the periphery of the head to provide the forgiveness of a cavity iron while having the thick feel of a muscleback with the unity of metal.
The thickness of the soft iron section behind the hitting point is well secured while providing the feel of a muscleback.
The soft S20C material is used for irons #5 to #7 in which titanium is built in, and the hard S25C material is used for irons #8 to PW in which titanium is not used. By using different soft iron materials with different hardness, consistent sound and feel across the irons were pursued.