I think rotorhead really means fire "resistant" clothing. Fire proof clothing would see cabin crew resembling overdressed oil rig fire fighters in the cabin (and they still wouldnt be fire proof) While wool/blends would seem to be the optimum, cotton is indeed a hazard in a fire.
The cynics would ask what the chances are of a flight attendant needing the benefits of a fire proof uniform, any more than a gas station attendant. Other cynics would ask when was last time it was a problem divided by the number of cabin crew cycles over the period.