"The tiles do a fantastic job of repelling heat, however they are very fragile and susceptible to impact damage."
"During the STS-87 mission, there was a change made on the external tank. Because of NASA's goal to use environmentally friendly products, a new method of "foaming" the external tank had been used for this mission and the STS-86 mission. It is suspected that large amounts of foam separated from the external tank and impacted the orbiter. This caused significant damage to the protective tiles of the orbiter. Foam cause damage to a ceramic tile?! That seems unlikely, however when that foam is combined with a flight velocity between speeds of MACH two to MACH four, it becomes a projectile with incredible damage potential."
The attention was now focused on the crew cabin cameras. These cameras gave more of a side view of the external tank as it tumbled back to Earth. These photographs revealed massive material loss on a side of the external tank that could not be viewed by the umbilical cameras!
"Where are we now? One of the questions had now been answered. The ascent phase of flight was when the damage occurred. With the information provided by the photography and the mapped flow of damage, a logical reason could be established as to "what" happened. It was determined that during the ascent, the foam separation from the external tank was carried by the aerodynamic flow and pelted the nose of the orbiter and cascaded aft from that point. Once again, this foam was carried in a relative air-stream between MACH two and MACH 4!"
http://216.239.33.100/search?q=cache:ryqlvTHKXEgC:ltp.arc.nasa.gov/space/team/journals/katnik/sts87-12-23.html+greg+katnik+tile+damage&hl=en&ie=UTF-8
I read every bit of that, and I do not concur that this is what brought the shuttle down.
The main reason for this assumption is that this tank and this insulation has been flown time and time again since STS-87. No unusual tile damage was reported from this effect. I cannot draw a conclusion on this data alone. I would like to see wind tunnel tests which we are quite capable of doing and I am sure it is in the works. That is why they wanted to try the insulation hypothesis and test it for voracity.