Potentially, one of the most powerful pieces of evidence that the WTC towers were brought down by controlled demolitions is the videos of a molten, orange/yellowish metal flowing from the south tower shortly before it collapsed. The pivotal question is, what king of metal was it? Those who do not accept the controlled demolition explanation claim that it was melted aluminum alloy from the burning plane. The problem with this explanation is that when melted aluminum, even when it appears orange/yellow when contained in a hot environment, is poured out into a cooler environment, it quickly turns silvery in color. The molten metal flowing from the south tower maintains its orange/yellow color for all or most of its descent.
If it isn't aluminum, then what kind of metal is it? And since the temperature of office fires or jet fuel fires wouldn't be hot enough to melt other metals that would be in great quantity in the towers, what would produce the great amount of heat necessary to melt whatever metal it is? If thermite or nanothermite was used in large quantities in controlled demolitions of the towers, then there would be a great deal of molten iron, which would maintain its orange/yellow color for a very long period of time. A good presentation of the evidence can be found at Debunking the Debunkers.