RDX is a remotely detonated explosive in The Saboteur.
Due to the ease of manufacture, RDX was widely used by both sides during World War II. Because it was a plastic explosive, it could be molded into many shapes and forms and would not be ruined when in contact with water. In addition, RDX will only detonate when triggered by the detonator and can't be ignited by even small arms fire.
In game, RDX is grey colored and costs 5 contraband from the Black Market. Unlike Dynamite, multiple RDX charges can be placed and remotely detonated anytime. Because of this, many players prefer RDX over Dynamite. In the Brymann mission where Sean is tasked with destorying the German seige gun, Sean recieves several RDX charges. RDX's explosive radius can be upgraded with purchase of the Sabotage upgrade in the Black Market shop.