ACDelco 4SD25X Professional Negative Battery Cable Tough cross-linked synthetic rubber insulator casing that resists burning, softening, or melting in high heat, and resists corrosion from chemicals and road splash 99% pure copper cables to maximize conductivity and quick cold weather starts Light weight for improved flexibility Steel skeleton embedded in casting for more reliable electrical connection Casting overlaps cable insulation to protect cable from corrosion, which is the primary cause of cable failure