  Rhenium foil. 
These are tiny little strips of rhenium foil about half an inch long.  If they were made of aluminum this would be a pile of fluffy shreds.  But it's rhenium, one of the hardest and densest elements, so instead it's a surprisingly heavy mass of fairly stiff strips. 
Source: eBay seller forsythia 
Contributor: Theodore Gray 
Acquired: 29 September, 2003 
Price: $16 
Size: 0.5" 
Purity: 99.9%
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