ISO FLEX is a Pivot designed, Patent Pending system that isolates the seatpost from the frame for extraordinary comfort while maintaining elite level frame stiffness. The lightweight rubber insert comes in two sizes: 27.2mm and 30.9mm allowing the rider to use any seatpost on the market including dropper posts with class-leading comfort. 27.2mm is included with the frame and the 30.9mm size is available for purchase through your local Pivot Cycles dealer.