C-4 or Composition C-4 is a powerful plastic explosive compound. It is composed of explosives, plastic binder, plasticizer and usually a marker or odorizing taggant chemical, such as 2,3-dimethyl-2,3-dinitrobutane (DMDNB) to help detect the explosive and identify its source.
The explosive force used in C-4 is RDX (cyclonite or cyclotrimethylene trinitramine), which makes up around 91% of C-4 by mass. The plasticizer is diethylhexyl (5.3%) or dioctyl sebacate and the binder is usually polyisobutylene (2.1%).
C-4 was used by Hans Gruber and his men to plant it underneath the roof of the Nakatomi Plaza building. They planned to use it to destroy the roof, killing the hostages and fooling police into thinking that the terrorists themselves were also killed in the explosion. But McClane intervened in their scheme and saved the hostages. Hans set off the explosions anyway, destroying the helicopter carrying FBI agents, but failing to kill the hostages or McClane, who tied a fire hose to his waist and jumped off the roof, away from the explosion.
Earlier in the film, after McClane killed Heinrich and Marco, he examined Heinrich's C-4 and eventually used it to kill Alexander and James who are both trying to destroy the SWAT armored RV with their rocket launcher by putting it on a chair and throwing it down an elevator shaft. This scene was inspired from a part in the book Nothing Lasts Forever, which also features C-4.
C-4 was used by Colonel Stuart and his men on the makeshift airport equipment at the church to ensure no one will use the equipment to land the planes.
C-4 is featured briefly in Live Free or Die Hard, where it is used to kill everyone unwittingly implicated in the Fire Sale. The featured 'hackers' are assumed to have installed a fail-safe system, where they have installed C-4 in their computers in a last attempt to delete incriminating or sensitive data. The terrorists are aware of this and send a computer virus to their computer; when they hit the delete key to try and restore their systems, their house explodes.
- C-4 on Wikipedia