2300F fireclay insulating soft brick. 9" x 4.5" x 2.5". Fired Analysis: SiO2-55%, Al2O3-42%, Fe2O3-.7%, KNa-1.1%. Density is 36 lbs./cubic foot. Modulus of rupture is 145 lbs./sq. inch. Thermal Conductivity at 2400F is .26.