Fiberfrax or Fiberfax is a silica & alumina material that comes in different densities as a blanket or in a more rigid board. It comes in different heat ratings up to 2600 I believe. It's not something you want to handle often as it's a class 2 carcinogen. It's often used between the kiln bricks and the metal jacket of electric kilns where there is less chance of the fibers getting airborne. It's also used inside raku kilns. There is a rigidizer you can brush or spray onto it to help keep the airborne fibers down. I wouldn't use it on the top of a kiln where you are lifting it on and off for every firing.
msds for one brand is here: http://www.fiberfrax...-MSDS-M0114.pdf