Polystyrene is a 
polymer made from 
styrene, a liquid that is found in plants but is commercially manufactured from 
petroleum.  Polystyrene was first manufactured by 
BASF in the 
1930s, and is used in numerous plastic products.  Its most common use, however, is as expanded polystyrene, which is a mixture of about 5% polystyrene and 95% air.  This is the material of which coffee cups and takeaway food containers are made.  In the 
USA it is made by the Dow Chemical Company under the tradename Styrofoam.
 
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