We measured the thermal conductivities of sapphire fibers, pure aluminum and copper wires, and a pure graphite sheet at cryogenic temperature. They were investigated as materials of heat conductors used at different temperature ranges for a cryogenic interferometric gravitational wave detector. The thermal conductivities of sapphire fibers (sub millimeter in diameter) were over 103W/(m·K) at around 40K. Below this temperature, we confirmed that they were limited by the sample diameter. The thermal conductivities of pure aluminum and copper wires were over 104W/(m·K) at around 10K, and were limited by internal defects in the samples. For the graphite sheet, the thermal conductivity was over 600W/(m·K) between 200K and 300K. It is effective as a heat conductor to reduce cooling-time of the system.
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