Cobra golf bio cell s senior flex irons bio cell irons are packed with game changing technologythe longest iron in this set is in fact a hybrid club and the mid irons feature heavy tungsten weights strategically positioned in the heel and toe for more forgiveness and the short irons have the tungsten positioned directly behind the hitting area for a solid feel optimal spin control and versatility as you approach the greenthe bio cell s irons also feature cobrarsquos largest unsupport