Are our members aware these machines (full body scanners) will not detect or show as an image the most popular explosives used by the terrorists? These explosives are RDX and PETN. I was very surprised to learn of this while watching a program on CNN. It seems as if the entire security exercise at our airports may be a waste of time. Both Semtex and C-4 contain two powerful explosives RDX and PETN [also known as cyclonite and pentaerythritol tetranitrate] but differ in the plastic binder material. The explosives RDX and PETN are manufactured worldwide. Plastic bonded explosives containing RDX and PETN and binders are manufactured in several other countries, and theft is possible resulting in the explosive following into the hands of terrorists. Iran is believed to manufacture plastic bonded explosives. By agreement, several countries that manufacture plastic bonded explosives (U.S., Canada, Austria) incorporate tracer materials to enable the explosive to be traced to the country of origin. When officials were asked if full body scanners would have detected the small quantity of explosives involved in the underpants incident Christmas 2009, they replied as follows. The indications are that given where the PETN was placed, there would have been a remote chance of its being detected. Scanners can certainly pick up metal objects including knives, but whether they could have detected powder plastic explosive such as the 3 oz of PETN is extremely doubtful. The kind of explosive the underwear bomber used was low-density and so probably wouldnt have shown up on the scanner.