C-4 or Composition C-4 is a common variety of the plastic explosive family known as Composition C, which uses RDX as its explosive agent. C-4 is composed of explosives, plastic binder, plasticizer to make it malleable, and usually a marker or odorizing taggant chemical.
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The explosive material in C-4 is cyclotrimethylene-trinitramine (C3H6N6O6), commonly called RDX (which stands for "royal demolition explosive" or "research development explosive").