CI4 stands for Carbon Interfusion with the 4 referring to the number of electrons in the Carbon atom. Ultimately, this means CI4 is reinforced Carbon Fiber. The new CI4+ is the next generation of Shimano's CI4 material and 250% stronger. It is over one and a half times stronger than their normal XT-7 graphite and is over 20% lighter and because it does not contain metal, it is impervious to rust. As a result of its strength and weight, Shimano is able to create an extremely lightweight reel with very precise tolerances.Shimano Stradic CI4+ Reels feature:• Ultra-lightweight CI4+ Frame, Sideplate and Rotor Construction• X-Ship• Paladin Gear Durability Enhancement• Propulsion Line Management System: Propulsion Spool Lip, SR One-Piece Bail Wire, Power Roller III, Redesigned Bail Trip, S-Arm Cam• Aero Wrap II Oscillation• SR-Concept: SR 3D Gear, SR Handle, SR One-Piece Bail Wire• S A-RB Ball Bearings• Aluminum Spool• S-Concept: S-Rotor, S-Guard, S-Arm Cam• Machined Aluminum Handle• Direct Drive Mechanism (Thread In Handle Attachment)• Round EVA Handle Grip• WP Drag (Waterproof Drag)• Maintenance Port• Fluidrive II• Floating Shaft• Dyna-Balance• Super Stopper II• Repairable Clicker• Approved for use in Saltwater• Rated for use with Mono, Fluorocarbon and PowerPro lines