Intumescent paint is a reactive coating, when exposed to high temperature, the fire resistant paint expands in a controlled manner to many times its original thickness, producing a carbonaceous char formed by a large number of small bubbles. The material forms an insulating layer which slows the temperature of the steel rising to a critical level. In ambient conditions the thin coating allows for the steel structures to maintain their usual form rather than being boxed in with a board or covered with fire spray.
