> Even cheap butyl gaskets will do a good job keeping out the constituents of a standard air mixture of gases. Any He leakage would thus cause a pressure differ

> Even cheap butyl gaskets will do a good job keeping out the constituents of a standard air mixture of gases. Any He leakage would thus cause a pressure differential, which will tend to prevent further outleakage of He (by countering the entropy gain from mixing He with the air outside). While this would probably be true for almost any other gas, Helium is devilishly small and can permeate through the metal over time. [0] [0] http://www.eevblog.com/forum/chat/helium-filled-10tb-harddrive/25/ http://www.eevblog.com/forum/chat/helium-filled-10tb-harddri...