A sock is a piece of clothing worn on the feet and often covering the ankle or some part of the calf. Some types of shoes or boots are typically worn over socks. In ancient times, socks were made from leather or matted animal hair. In the late 16th century, machine-knit socks were first produced. Until the 1800s, both man-made and machine-knit socks were manufactured, but the latter technique become more common in the 19th century. One of the roles of socks is absorbing perspiration. As the foot is among the heaviest producers of sweat in the body, it can produce over 0.25 US pints (0.12 l) of perspiration per day; socks help to absorb this sweat and draw it to areas where air can evaporate the perspiration. In cold environments, socks made from cotton or wool help warm up cold feet which in turn, helps decrease the risk of getting frostbite. Thin socks are most commonly worn in the summer months to keep feet cool. Light colored socks are typically worn with sports shoes and dark colored socks with dress shoes (often black or navy blue dress socks). In addition, dark colored socks absorbs heat which in turn helps keep the foot warm while light colored socks reflects heat which in turn helps the feet stay cool.