[en] The permeabilities of helium through the pyrocarbon coatings of BISO HTGR fuel particle Batches OR2263HT, OR2269HT, J596, J598, J605, and J606 prepared by the Metals and Ceramics Division, Oak Ridge National Laboratory have been measured over the temperature range of 450 to 1200⁰C. These measurements were analyzed in terms of a simple diffusion model whereby the porosity of the pyrocarbon coating, the frequency factor term for diffusion (D₀), and the activation energy for diffusion were determined. The batch-to-batch variations in permeability ranged over a factor of 57 from the least permeable (J596) to the most permeable (J598). The major contribution to this variability was D₀ (1 x 10^-7 to 5 x 10^-6 m²s^-1) with porosity (1 to 5%) being second most important. The activation energy for diffusion (103 to 123 Kj mol^-1) displayed the least effect (approximately a factor of 2) on the batch-to-batch variability in the helium permeability