2600F fireclay insulating soft brick. 9" x 4.5" x 2.5". Fired Analysis: SiO2-41%, Al2O3-56%, Fe2O3-.7%, KNa-1.7%. Density is 50 lbs./cubic foot. Modulus of rupture is 220 lbs./sq. inch. Thermal Conductivity at 2400F is .36.