Supra Speaker Cables from the UK's Number 1 Supplier of Audio Visual cables. The Supra concept for cleaner sound. The tin is of higher resistance than copper and also protects copper from bad sounding corrosion. It also minimises the current jumps from wire to wire over corroded copper surfaces while more of the signal passes through the pure copper inside the wires. The tin layer also minimises the skin-effect by acting as a semi-litz.