Fire resistive materials: contain chemically bound water, in solid form. The concept is fundamental and taught in high school level chemistry. The chemically bound water is turned from solid directly to steam. The steam, at about 100°C is significantly colder than the fire. Thus the released steam is sent as a cooling vapour towards the energy source (fire). If one places an endothermic substance between the fire and something, which one desires to protect from the fire, the endothermic material will slowly but surely be spent. The more fire, the more steam is released and the less is left to protect the unexposed side. While any quantity of bound water is still left to protect the unexposed side, the temperature of the unexposed side cannot be raised above 100°C. Once the endothermic layer is spent, the heat on the unexposed side will rise. Thus, particularly in fireproofing tests, where one plots thermocouple readings of the unexposed side, one can immediately see a rise in temperature, from the ambient room temperature, towards the 100°C mark, where readings will sit and hover until such time as the water in the assembly is all spent. The trick in such testing is to guesstimate this timing such that one uses just the right amount of the protective endothermic material, to keep the unexposed side below the 140°C average rise as well as the maximum single hot spot rise of 180°C, which parallels many test procedures for assorted fire resistive products and systems, including firestops