C-4 is made up of explosives, plastic binder, plasticizer and, usually, marker or odorizing taggant chemicals such as 2,3-dimethyl-2,3-dinitrobutane (DMDNB) to help detect the explosive and identify its source.
As with many plastic explosives, the explosive in C-4 is RDX (cyclonite or cyclotrimethylene trinitramine), which makes up around 91% of C-4 by weight. The plasticizer is diethylhexyl or dioctyl sebacate (5.3%) and the binder is usually polyisobutylene (2.1%).
C-4 is manufactured by combining the noted ingredients with binder dissolved in a solvent. The solvent is then evaporated and the mixture dried and filtered. The final material is an off-white solid with a feel similar to modelling clay. It has a faint bituminous odor and an astringent taste.
C-4 detonation velocity is 8,040 m/s (26,400 ft/s), or 28,900 km/h (18,000 mph).
C-4 is often used in demolition charges such as the M183 and M112. The Demolition charge M183 is used primarily in breaching obstacles or demolition of large structures where large charges are required (satchel charge). The M183 charge assembly consists of 16 M112 block demolition charges, four priming assemblies, and M85 carrying case. Each Priming assembly consists of a five-foot length of detonating cord assembled with two detonating cord clips and capped at each end with a booster. The components of the assembly are issued in the carrying case. The demolition charge M112 is a rectangular block of Composition C-4 approximately 2 inches (51 mm) by 1.5 inches (38 mm) and 11 inches (280 mm) long, weighing 1.25 lb (0.57 kg). When the charge is detonated, the explosive is converted into compressed gas. The gas exerts pressure in the form of a shock wave, which demolishes the target by cutting, breaching, or cratering.
Using explosives provides the easiest and fastest way to break frozen ground. Composition 4, tetrytol, and TNT are the best explosives for use in northern operations because they retain their effectiveness in cold weather. Digging a hole in the ground in which to place the explosive and tamping the charge with any material available is done to increase its effectiveness. Either electric or nonelectric circuits may be used to detonate the charge. For a "foxhole", 4.6 kg (10 lb) of explosive will usually be sufficient. Another formula is to use 2 pounds (1 kg) of explosive for every 1 ft (30 cm) of penetration in frozen water (ice).
A major advantage of C-4 is that it can easily be molded into any desired shape. C-4 can be pressed into gaps, cracks and voids in buildings, bridges, equipment or machinery. Similarly, it can easily be inserted into empty shaped charge cases of the type used by military engineers.
C-4 is very stable and insensitive to most physical shocks. Detonation can only be initiated by a combination of extreme heat and a shock wave, as when a detonator inserted into it is fired. C-4 cannot be detonated by a gunshot or by dropping it onto a hard surface.
C-4 burns slowly when it is ignited with a flame rather than detonated with a primary explosive, so soldiers during the Vietnam War era would sometimes use small amounts of C-4 as fuel for heating rations while on long patrols. Burning C-4 produces poisonous fumes and should be avoided (see below). While many soldiers used C-4 safely in this manner, there are anecdotes about soldiers trying to put out the fire by stamping on it — causing it to detonate. These are untrue as a blasting cap is required for detonation.
Michael Herr in Dispatches, his book about the Vietnam War, relates that a soldier would occasionally ingest C-4 from a claymore mine in order to cause temporary illness and be sent on sick leave. Although the ruse might work with an inexperienced commander, experienced officers were usually aware of the trick and would keep the man on board.
These applications of C-4 are dangerous and could be deadly. US Army Field Manual 5-250, Explosives and Demolitions includes this bold print, block warning: "WARNING Composition C-4 explosive is poisonous and dangerous if chewed or ingested; its detonation or burning produces poisonous fumes."
The British military uses a plastic explosive referred to as PE4. Like C-4, it is an off-white coloured solid and its explosive characteristics are nearly identical to C-4. The type and proportion of plasticizer used differs, and PE4 has a more rapid velocity of detonation, 8210 metres per second.
Very similar to the British PE4 is the Italian military plastic explosive T4.