Semtex is a general-purpose plastic explosive. It is used in commercial blasting, demolition, and in certain military applications. Semtex became notoriously popular with terrorists because it was, until recently, extremely difficult to detect. Semtex was invented in the late 1950s by Stanislav Brebera, a chemist at VCHZ Synthesia, former Czechoslovakia. The explosive is named after Semtín, a suburb of Pardubice in the Czech Republic where the mixture was first manufactured starting in 1964. The plant was later renamed to become Explosia a.s., a subsidiary of Synthesia.
Semtex was very similar to other plastic explosives, especially C-4, in that it was easily malleable; but it was usable over a greater temperature range than other plastic explosives, as it stays plastic between −40 and +60 °C; it is also waterproof.
The new explosive was widely exported, notably to the government of North Vietnam, which received 14 tons during the Vietnam War. However, the main consumer was Libya; about 700 tons of Semtex were exported to Libya between 1975 and 1981 by Omnipol. It has also been used by Islamic militants in the Middle East and by the Provisional Irish Republican Army (IRA) and the Irish National Liberation Army in Northern Ireland.
Exports fell after the name became closely associated with terrorist attacks. Export of Semtex was progressively tightened and since 2002 all of Explosia's sales have been controlled by a government ministry. Also in response to international agreements, Semtex has a detection taggant added to produce a distinctive vapor signature to aid detection. According to the manufacturer, the taggant agent was voluntarily being added by 1991, years before the protocol signed became compulsory. The shelf life of Semtex was reduced from 10 years before the 1990s to five years now. Explosia states that there is no compulsory tagging allowing reliable post-detonation detection of a certain plastic explosive (such as incorporating a unique metallic code into the mass of the explosive), so Semtex is not tagged in this way.