Part of the key to optimizing that MOI and head size is the thinnest crown on a fairway wood in Callaway’s history. But the meat of the XR16’s design is Callaway’s trademark face cup design, where the face wraps around both the front of the crown and sole to expand the area of the face that provides the most spring-like effect. The high-strength forged Carpenter 455 steel alloy in the face cup gets as thin as .043 inches at the perimeter to improve flexibility. That’s the thinnest face the company has designed.