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. Common plastic explosives include Semtex and C-4. Plastic explosives are especially suited for explosive demolition as they can be easily formed into the best shapes for cutting structural members and have a high enough velocity of detonation and density for metal cutting work. They are generally not used for ordinary blasting as they tend to be significantly more expensive than other materials that perform just as well in that field. Also, when an explosive is combined with a plasticizer, its power is generally lower than when it is pure.
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Plastic explosive is commonly used for the demolition of obstacles and fortifications by engineers and combat engineers, an early use being the warhead of the British Armoured Vehicle Royal Engineers's (AVRE)'s 'Petard' demolition mortar, used to destroy concrete fortifications encountered during Operation Overlord (D-Day). The original use of Nobel 808 not supplied by the SOE was for sabotage of German installations and railways in Occupied Europe. The most common commercial use of plastic explosives is for shock hardening high manganese percentage steel. This material is typically used for train rail components and earth digging implements.
Some terrorist groups have used plastic explosives. In October 2000, al-Qa'ida used C-4 to attack the USS Cole, killing 17 sailors In 1996, terrorists used C-4 to blow up the Khobar Towers U.S. military housing complex in Saudi Arabia.
Prior to World War I, the British explosives chemist Oswald Silberrad obtained British and U.S. patents for a series of plastic explosives called "Nitrols", composed of nitrated aromatics, collodion, and oxidising inorganic salts. The language of the patents indicate that at this time, Silberrad saw no need to explain to "those versed in the art" either what he meant by plasticity nor why it may be advantageous, as he only explains why his plastic explosive is superior to others of that type.
One of the simplest plastic explosives was Nobel's Explosive No. 808, also known as Nobel 808 (often just called Explosive 808 in the British Armed Forces during the Second World War), developed by the British company Nobel Chemicals Ltd well before World War II. It had the appearance of green plasticine with a distinctive smell of almonds. During World War II it was extensively used by the British Special Operations Executive (SOE) for sabotage missions. It is also the explosive used in HESH anti-tank shells. Captured SOE-supplied Nobel 808 was the explosive used in the failed 20 July plot assassination attempt on Adolf Hitler in 1944.
During and after World War II a number of new RDX-based explosives were developed, including Compositions C, C2, and eventually C3. Together with RDX these incorporate various plasticisers to decrease sensitivity and make the composition plastic. The origin of the obsolete term plastique dates back to the Nobel 808 explosive introduced to the U.S. by the British in 1940. The samples of explosive brought to the U.S. by the Tizard Mission had already been packaged by the SOE ready for dropping to the French Resistance and were therefore labelled in French, as Explosif Plastique. It is still referred to by this name in France and also by some Americans.
C3 was effective but proved to be too brittle in cold weather. In the 1960s it was replaced by C-4, also using RDX but with polyisobutylene and di(2-ethylhexyl)sebacate as the binder and plasticizer.
List of plastic explosives 
- Austria: KAUERIT
- Czech Republic: Semtex-H (orange colored), Semtex 1A (red colored), NP10 (black colored)
- Finland: PENO
- France: PE4, PLASTRITE (FORMEX P 1)
- Germany: Sprengkörper DM12, (Sprengmasse, formbar)
- Netherlands: Knaverit S1 (light orange colored)
- Greece: C3, C4
- Italy: T-4 Plastico
- Norway: NM91(HMX), C4
- Poland: PWM, NITROLIT
- Russia: PVV-5A Plastic Explosive
- Slovakia: CHEMEX (C4), TVAREX 4A, Danubit
- Sweden: Sprängdeg m/46
- Switzerland: PLASTITE produced by SSE
- USA: C-4 (Pure White)(Composition C-4)
- United Kingdom: PE4 (off-white colored), DEMEX (sheet explosive)
- Yugoslavia/Serbia: PP–01 (C4)
- Cooper, Paul W. (1996). "Chapter 4: Use forms of explosives". Explosives Engineering. Wiley-VCH. pp. 51–66. ISBN 0-471-18636-8.
- Explosive Hardening, PA&E, Inc.
- Whitaker, Brian (Thursday 21 August 2003 09.00 BST). "Bomb type and tactics point to al-Qaida". The Guardian (London: Guardian Media Group). Retrieved July 11, 2009.
- US Patent # 1092758