Intumescent coatings are specialized paints or sprays applied to structural elements, typically steel or timber, to enhance their fire resistance. When exposed to the intense heat of a fire, these coatings undergo a chemical reaction, swelling significantly to form a thick, insulating, carbonaceous char layer. This char layer acts as a barrier, protecting the underlying substrate from the heat of the fire and slowing down the rate at which the material heats up.

For steel, this is crucial as it maintains the steel's structural integrity, preventing it from reaching critical temperatures where it loses strength and collapses. For timber, it delays ignition and reduces flame spread. The thickness of the intumescent coating is calculated based on the required fire resistance period and the characteristics of the structural element.