Asked by Anonymous on February 13th, 2018.
We are unsure what the leads are made of but the Sozo caps have tin coated pure copper. We suspect these are the same or of similar quality.
I don' t know the exact alloy by number or anything but nearly al (all?), common through hole components have tinned copper clad steel leads. Pure copper is used for the cladding but pure copper leads would be much too soft and could not survive the mechanical bending twisting, folding etc., that components go through during fabrication and the assembly process of the devices they are used in. Also wire made purely from copper would conduct heat too well, damaging the insides of capacitors and resistors