Method and apparatus for replenishing an inert gas atmosphere. A replenishment structure includes a reservoir which encloses an internal inert gas atmosphere. The reservoir has a permeable wall through which inert gas molecules from the internal atmosphere diffuse substantially at a first rate. A control material adjacent the reservoir provides a path through which the inert gas molecules further diffuse substantially at a second rate less than the first rate to replenish a surrounding inert gas atmosphere. The control material preferably surrounds or otherwise confines the reservoir, and diffuses the molecules at a rate selected in relation to which inert gas molecules from a surrounding gas atmosphere escape from a housing in which the replenishment structure is disposed. The permeable wall preferably comprises glass and the inert gas preferably comprises helium. As desired, the inert gas molecules can further be diffused through a second control material to the surrounding atmosphere.