Temperature dependence of the leak rate and permeability of helium gas through Kapton foils

The leak rate of helium gas through thin Kapton HN foils was measured for various temperatures between 310 and 150 K and gas pressures ranging from 10 to 300 mbar. From these measurements the permeability constant P(T) and its temperature dependence were determined. At room temperature the permeability constant for Kapton HN is P ( T =296 K ) = ( 2.56 ± 0.31 ) barrer. The temperature dependence of P(T) was verified to drop exponentially with decreasing temperature, causing a change in the permeability by more than two orders of magnitude in the range between 310 and 150 K.