This is a Shimano Polymer Coated Road Brake Inner Cable. This cable is for use with the BR-9000 and BR-9010 brakes.
Stainless steel for anti-rust protection
Polymer-coated inner cable reduces the sliding resistance to achieve lighter and quicker operation
Approved by Shimano only for use with Dura-Ace BR-9000/9010, Ultegra BR-6800/6810 & Cyclocross BR-CX70
Low friction polymer material on the cable may cause slippage at the cable fixing bolt after initial pre-stretch for the cable is performed. Fur like material from polymer coating will not effect the performance
Buying Guide - Handbook
What to look for and things to consider before you buy