Indium foil like this is typically used in high-vacuum systems to form a seal between glass components. It is soft enough to squeeze into the glass surfaces and form a perfect seal. Unlike rubber, it does not give off gases of its own, or allow air to diffuse through slowly.
Source: eBay seller assetrecoveryctsystems
Contributor: Theodore Gray
Acquired: 24 February, 2007
Text Updated: 29 January, 2009