The coat of the domestic dog (Canis lupus familiaris) refers to the hair that covers its body. A dog's coat may be a double coat, made up of a soft undercoat and a coarser topcoat, or a single coat, which lacks an undercoat. Double coats have a top coat, made of stiff hairs to help repel water and shield from dirt, and an undercoat to serve as insulation.