The key change in the X Hot iron lies underneath the surface

Callaway Golf calls its X Hot set "aggressive irons" that produce "measurable distance gains" over previous generation Callaway irons. In the X Hot irons, Callaway takes the "Speed Frame Face Technology" it's been using in its drivers and utilized it in irons. That tech is designed to create a better transfer of energy from clubface to golf ball, thereby boosting ball speed and distance performance. These irons also use a Deep Undercut Cavity design to move the center of gravity lower (helping with launch) and move the "hottest" part of the clubface lower, as well.