What characteristic do intumescent coatings possess?

Intumescent coatings are specifically designed to provide fire retardancy. When exposed to high temperatures, these coatings undergo a chemical reaction that results in the formation of a thick, insulating char. This char acts as a barrier, protecting the substrate material underneath from sustaining damage due to fire. The primary function of intumescent coatings is to slow down the spread of flames and heat, allowing more time for evacuation and helping to prevent structural collapse in case of a fire.

In contrast to other options, while water-repellency, UV resistance, and chemical resistance are beneficial characteristics that coatings may possess, they are not the defining feature of intumescent coatings. The key attribute of these coatings lies in their ability to expand and insulate when exposed to heat, thus serving a critical role in fire protection.