C-4 is made up of explosive, binder, plasticizer and (latterly) marker or taggant chemicals. As in many plastic explosives the explosive material in C-4 is RDX (Cyclonite, cyclotrimethylene trinitramine) which makes up around 90% of the C-4 by weight. The binder is polyisobutylene (5.5%) and the plasticizer is di(2-ethylhexyl) or dioctyl sebacate (2%). In the US the marker is DMDNB (2, 3-dimethyl-2, 3-dinitrobutane). Another binder used is dioctyl adipate (DOA). A small amount of petroleum oil is also added.
C-4 is made by combining a RDX slurry with the binder dissolved in a solvent. The solvent is then removed and the mixture is dried and filtered. The final material is an off-white solid with the feel of soft clay.
C-4 is an development of a WW II material that mixed RDX with mineral oil and lecithin to achieve roughly the characteristics of plastic explosive but with certain disadvantages. C-4 is part of a group of explosives along with C, C-2 and C-3, each containing different amounts of RDX developed in the 1960s.
The C is sometimes said to stand for composition and the name is an abbreviation of Composition 4. However, composition is used for any castable explosive and composition A and composition B are also known variants. Therefore correctly C-4 is Composition C-4.