Srixon included their proprietary Rebound Frame which has two zones that flex at impact: one is the variable thickness face and the second a flexibility zone away from the face that bulges outward at impact. When the zones return to shape energy transfer is increased and a 10% higher COR gives added yards. The inner lattice design crown construction is called a Star Frame for added stability. $499.99
https://us.dunlopsports.com/srixon/clubs/irons/zx5-mk-ii-irons/zx5-mk-ii-irons/MZX5MKIIIRN.html
