A boot, plural boots, is a type of specific footwear. Most boots mainly cover the foot and the ankle, while some also cover some part of the lower calf. Some boots extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is clearly distinguishable from the rest of the sole, even if the two are made of one piece. Traditionally made of leather or rubber, modern boots are made from a variety of materials. Boots are worn both for their functionality – protecting the foot and leg from water, extreme cold, mud or hazards or providing additional ankle support for strenuous activities with added traction requirements, or may have hobnails on their undersides to protect against wear and to get better grip; and for reasons of style and fashion.