  We have made thermal and electrical transport measurements of uncompressed
pyrolytic graphite sheet (uPGS), a mass-produced thin graphite sheet with
various thicknesses between 10 and 100 {\mu}m, at temperatures between 2 and
300 K. Compared to exfoliated graphite sheets like Grafoil, uPGS has much
higher conductivities by an order of magnitude because of its high
crystallinity confirmed by X-ray diffraction and Raman spectroscopy. This
material is advantageous as a thermal link of light weight in a wide
temperature range particularly above 60 K where the thermal conductivity is
much higher than common thermal conductors such as copper and aluminum alloys.
We also found a general relationship between thermal and electrical
conductivities in graphite-based materials which have highly anisotropic
conductivities. This would be useful to estimate thermal conductance of a
cryogenic part made of these materials from its electrical conductance more
easily measurable at low temperature.
