(CNN) -- The Christmas Day airline terror alert has brought focus on PETN, a substance till now largely unknown to the public.
The white powder is said to be central to the alleged plot by Umar Farouk AbdulMutallab to bring down a passenger aircraft, carrying 300 passengers, as it prepared to land in Detroit. But just what is PETN?
What does PETN look like?
Pentaerythritol tetranitrate, to give it its full name, is a fine white powder that resembles sugar or salt. It does not compress down very well.
How easy is to obtain?
The core chemical in PETN is hard to make or get your hands on.
How volatile is PETN?
Not very. Although it is an explosive, you have to hammer it or ignite it to make it go off. And since it is not volatile, it is perfect for a terrorist on a long haul flight.
As Sidney Alford, a UK explosives expert, explained to CNN's senior international correspondent Nic Robertson: "It wouldn't go off accidentally. If I was carrying a pocketful of just neat powder in my pocket, it blowing up would be the last of my worries."
How much PETN did alleged bomber AbdulMutallab possess?
Sources familiar with the investigation tell CNN the working assumption is that AbdulMutallab may have had some 80 grams of PETN. Alford says that this would be enough to blow a hole in an aircraft.
What will PETN do when ignited?
Alford conducted a controlled explosion of a sample of PETN for CNN.
Six grams of PETN -- less than a tenth of what AbdulMutallab is alleged to have had in his possession -- punched a large circular dent into a metal plate twice the thickness of an aircraft fuselage.
Alford said that he would usually expect six grams to punch a hole through the plate. He said it failed to happen on this occasion because half of the PETN burnt off before the explosion itself; also thick ice under the plate would have softened the impact of the blast.
AbdulMutallab is said to have had much more than six grams. But, it is alleged, he didn't have the expertise to detonate it.
How easy is PETN to conceal?
CNN understands that alleged bomber AbdulMutallab was wearing explosives in the groin area. The appearance of PETN makes it easy to imagine how it can be stitched into clothing hidden around the body.
Alford says that it is possible to sew PETN into a set of underpants. "I've done it," he says, "no problem at all."
He also added: "A great potential advantage of powdered PETN is that it could look like a wide range of substances or be disguised as even more -- whereas plastic explosives do look suspiciously like plastic explosives."
Given its appearance and ability to be concealed, PETN is a challenge for airport security officials to detect through usual means such as a metal detector.
A statement attributed to al Qaeda in the Arabian Peninsula, dated Saturday and published Monday on radical Islamist Web sites, claimed responsibility for the attempted terrorist attack.
It said it tested "new kind of explosives" in the alleged plot and hailed the fact that the explosives "passed through security."
"There was a technical problem that resulted in a non-complete explosion," the message said.
Why did the PETN that AbdulMutallab allegedly possessed fail to explode?
Alford believes the only reason lives were spared this time is because the alleged bomber's lack of training meant he couldn't detonate the bomb. That means he probably did not make it.
As Alford explains: "On the one hand he's been given a high value substance. On the other hand he's been left to his own efforts.
"I would expect someone knowledgeable and disciplined enough to make PETN would have been equally careful and assiduous in his means of initiating it."
CNN's Nic Robertson contributed to this report.