The design of shoes has varied enormously through time and from culture to culture, with appearance originally being tied to function. Additionally, fashion has often dictated many design elements, such as whether shoes have very high heels or flat ones. Contemporary footwear in the 2010s varies widely in style, complexity and cost. Basic sandals may consist of only a thin sole and simple strap and be sold for a low cost. High fashion shoes made by famous designers may be made of expensive materials, use complex construction and sell for hundreds or even thousands of dollars a pair. Some shoes are designed for specific purposes, such as boots designed specifically for mountaineering or skiing. Traditionally, shoes have been made from leather, wood or canvas, but in the 2010s, they are increasingly made from rubber, plastics, and other petrochemical-derived materials. Though the human foot is adapted to varied terrain and climate conditions, it is still vulnerable to environmental hazards such as sharp rocks and temperature extremes, which shoes protect against. Some shoes are worn as safety equipment, such as steel-soled boots which are required on construction sites.