Please don't shoot the messenger, but I am posting this response I received from a spokesman for the Fibrament folks. I thought it only right someone there had a chance to present their data.
"I am disappointed to learn red.november used incorrect data to evaluate our FibraMent Baking Stone. It is apparent this person does not have the knowledge or academics to correctly compare our FibraMent Baking Stone to the ceramic cordierite.
FibraMent is specifically manufactured for commercial and home baking stone use. Cordierite is primarily used as kiln furniture and for applications in steel mills and foundries. Cordierite is available in many formulas. What grade of cordierite did red.november use for his evaluation?
We send our FibraMent Baking Stone to CTL in Skokie, IL for testing. They are internationally respected testing laboratory. The heat transfer/thermal conductivity rating (k factor) for FibraMent is 5.6 Btu. in./hr. sqft. F. I do not know why red.november would dispute the lab's results.
It is common knowledge in our field that higher density materials have lower thermal shock values. The dry density of our material is 126 lbs pcf.
To increase FibraMent's strength we place several layers of high temperature fabric in the matrix. Cordierite does not use any type of fiber or fabric to increase its tensile, flexural or compressive strength.
The Compressive Strength for FibraMent is 10,630 psi per ASTM C 109. Our Flexural Strength (Modulus of Rupture) is 1535 psi per ASTM C 78. Compressive Strength does not have anything to do with heat transfer.
red.november also has the maximum temperature rating for FibraMent incorrect. It appears red.november is only trying to discredit FibraMent. The maximum temperature rating for FibraMent is 1500 F/815 C. The maximum temperature rating is independent of heat transfer. Baking stones are typically used at temperatures from 350 to 600 F. It is not necessary for baking stones to have a temperature rating that exceeds 750 F.
Thank you for bringing this to my attention. Please feel free to post my reply on that web site.