The Kimber Kable Silver Streak XLR Balanced interconnect uses silver for both the positive and return leg, and copper for the ground. The RCA Single-Ended version on the other hand uses silver for the positive leg only, copper for both return and ground.
The Kimber Select (higher priced) line uses a mix of silver and copper in each leg in some of the models, pure copper or pure silver in others. The higher the silver content, the higher the price, of course.