Refractory Materials for Casting
These two products can stand up to the heat in a wood-burning device. Otherwise, their characteristics and uses are opposite from each other. The conductive refractory transmits heat and stores it for later release. The insulative refractory reluctantly conducts heat; it has some structural strength and can be used to protect wood floors, etc.
The two materials come in the same size bag. You can tell something about them by the comparative weight of the bags.