TaylorMade Burner 1.0 Iron Set (#4 thru PW, AW): Right, Burner SuperFast 85 Steel (Uniflex) A multi-functional sole with beveled edges reduces turf resistance to deliver maximum force to the ball at impact Inverted Cone Technology expands the area on the clubface that delivers higher ball speed, resulting in more consistent distance from shot to shot Progressive face thickness and head shape and size make every Burner iron uniquely powerful. COR and MOI have been optimized in every iron