Most of the weight of a Glock is steel.
Detectable by metal detectors.
A plain Glock frame: no slide, no barrel, no firing mechaism, no metal parts, will pass a metal detector. Without a slide, barrel and firing mechanism, it is useless as a weapon. Jack Anderson made a BFD out of slipping a stripped Glock frame past the metal detector at Congress, which just proved to me he was a BSing SOB.
When Anderson made a big publicity splash sneaking the polymer frame past the metal detectors NRA persuaded all manufacturers of "plastic" guns to include barium in the polymer mix do they would show up as fully delineated guns on Xray.
The idea that a plastic frame with no barrel, etc., can slip past a metal detector is dumb. A toothbrush with a sharpened handle can slip past a metal detector too and is a deadlier weapon than the plastic frame of a Glock (or any other polymer frame gun).
The media lie constantly to promote gun control, and true believers in gun control do not care about the truth. They have constantly repeated the same lies since the 1960s because of their agenda.