PETN (pentaerythritol tetranitrate) is a powerful plastic explosive. It belongs to the same chemical family as nitroglycerin. A few ounces can blast open an airplane, so it is the preferred weapon of terrorists.
PETN is a common legal explosive, used by the military as well as industries such as mining, where it is mostly used in detonator cord or in devices to ignite another compound. In addition to powder, the material is manufactured in thin plasticized sheets.
Regulations in the U.S. and many other countries make it difficult to buy PETN and other explosives off the shelf.
Residue from PETN powder is easily detectable with swabs that security personnel often use to wipe off briefcases, luggage and other personal items taken through airport checkpoints.
On Christmas Day 2009 Umar Farouk Abdulmutallab, a 23-year-old Nigerian, on Northwest Airlines Flight 253 to Detroit from Amsterdam carried PETN but failed to detonate it. The plane was carrying more than 300 people.
Abdulmutallab tried to ignite a two-part concoction of PETN and possibly a glycol-based liquid explosive. It set off popping, smoke and some fire but no deadly detonation, because he used the wrong technique.