Ben Wallace, the Conservative MP, formerly involved in a project to develop whole body scanners for airport use, said trials had shown that such low-density materials went undetected — such low density materials as those used by Umar Farouk Abdulmutallab, 23, who had concealed in his underpants a package containing nearly 3oz of the chemical powder PETN (pentaerythritol tetranitrate).
Wikipedia: Security Scan (Whole Body Scanner) | PETN | Umar Farouk Abdul Mutallab | UK MP Ben Wallace