CuSil is a brand name for an alloy of 72% silver and 28% copper, that was once thought to have better properties than silver alone. According to Mr. Toshi Oyama, Ph.D. R&D Manager, WESGO Metals, "the thermal conductivity of Cusil was calculated from Electrical conductivity, which is reasonable since both are controlled by free electrons in metals. However, electrical conductivity of Cusil was measured about 30 years ago with a very primitive machine. I re-measured it, and calculated Cusil thermal conductivity to be 371 W/m/K."