Poor Fireproofing Brought Down WTC, Top NIST Adviser SaysSPECIAL REPORT: Poor fireproofing brought down the World Trade Center, a top NIST adviser says. Ten years after 9/11, some of the nation's leading engineers speak out for the first time, saying the spray on foam insulation used on the Twin Towers simply wasn't thick enough. If enough material had been on the building, it would still be standing today, they say. "One could say the building was poorly designed."