XCH-3B, hard tension, is a classical halfset made up of D'Addario's proprietary EXP coated silver plated copper wound on a multifilament composite core for a familiar feel and enhanced string life. EXP classical half sets are the most natural-sounding, longest-lasting coated strings available. Each bass is wound with the highest quality wrap wire materials, precision drawn and micro coated on our advanced proprietary machinery. The ultra-fine layer of EXP Coating is bonded to the silver-plated copper wrap wire which is then wound onto a multi-filament core resulting in a natural round wound feel and sound fresh and bright with a "new string tone" that lasts three to four times longer than traditional strings.