C4 or Composition C4 is a common variety of the plastic explosive

Plastic explosive

Plastic explosive is a specialised form of explosive material. It is a soft and hand moldable solid material. Plastic explosives are properly known as putty explosives within the field of explosives engineering....

 known as Composition C

Composition C

The Composition C family is a family of related US-specified plastic explosives consisting primarily of RDX. All can be moulded by hand for use in demolition work and packed by hand into shaped charge devices. Variants have different proportions and plasticisers and include C-2, C-3, and C-4.The...

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C4 is made up of explosives, plastic binder, plasticizer

Plasticizer

Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...

 and usually marker or odorizing taggant

Taggant

A taggant can mean a radio frequency microchip used in automated identification and data capture . In such cases, electronic devices use radio waves to track and identify items, such as pharmaceutical products, by assigning individual serial numbers to the containers holding each product...

 chemicals such as 2,3-dimethyl-2,3-dinitrobutane (DMDNB

DMDNB

DMDNB, or also DMNB, chemically 2,3-dimethyl-2,3-dinitrobutane, is a volatile organic compound used as a detection taggant for explosives, mostly in the United States where it is virtually the only such taggant in use. Dogs are very sensitive to it and can detect as little as 0.5 parts per billion...

) to help detect the explosive and identify its source.

The explosive in C4 is RDX

RDX

RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...

 (cyclonite or cyclotrimethylene trinitramine), which makes up around 91% of C4 by mass.