Styrofoam is never biodegradable. However, some packing peanuts are now made of extruded wheat paste and brightly colored with food dyes. They generally are more compressible than Styrofoam peanuts and have less rebound after being squished, but since they are made of wheat, completely biodegradable. In fact, they melt and dissolve away completely when exposed to water, being nothing but extruded wheat paste. Styrofoam, on the other hand, is completely impervious to water.
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Helice
Nemo me impune lacesset.
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"Of all the tyrannies that affect mankind, tyranny in
religion is the worst; every other species of tyranny is
limited to the world we live in; but this attempts to
stride beyond the grave, and seeks to pursue us into
eternity."
-- Thomas Paine