The Callaway Big Bertha Fusion Irons incorporate the Company's uniquely superior, weight-shifting Fusion Technology ' the same revolutionary science featured in the ERC Fusion Drivers and Fairway Woods. Big Bertha Fusion Irons have a clean, traditional look, yet deliver unprecedented playability, performance and confidence. At the heart of Fusion Technology in the new Big Bertha Fusion Iron design is the Tunite alloy cradle. Callaway Golf designers created a completely new, patented alloy for the cradle that is ultra-dense and allows 77% of the clubhead mass to be repositioned to the perimeter of the head. This extreme perimeter weighting creates a very high Moment of Inertia (MOI) for significantly greater resistance to twisting and exceptional stability on all types of shots. The Tunite alloy cradle works in tandem with a lightweight, 6-4 titanium face insert that is strong, efficient and 35% lighter than a comparable steel face ' which frees mass to be distributed around the clubhead perimeter. The final piece of the Big Bertha Fusion Irons design is TPU SenSert; an exclusive, chemically engineered thermoplastic urethane material is in the back cavity of the iron. It works in tune with the clubface to reduce vibration at impact and give shots a crisp, responsive sound and unmatched feel. The end result is a traditional-looking iron with a high-technology, high-lustre appearance that gives golfers of all ability levels confidence at address while maintaining the benefits of an oversize, game improvement iron.