In order to provide the best sounding performance, WEET upgrade lead from tinned copper wire to gold/silver copper wire.
This improvement are highly welcomed for high end audio application manufacturer, thank you.
https://www.musicaps.com/product/WEET-WMT-Silver-Gold-Tinned-Copper-Wire-Condenser-Audio-Grade-MKP-Capacitors.html

Quick transient design

High Precise Capacitance ±2%, ±3%, ±5%

Very Low Dielectric absorption factor Very Low Dissipation factor, Very Low ESR,

Very Low Inductance Excellent handling of high current audio pulses

The gold-plated copper leads provide long-term high reliability and excellent solder ability