Skin refers to the finishing of skis intended for ski mountaineering or touring, where special bands are attached to the underside of the skis to improve their climbing ability when moving on hilly terrain. These 'skins' are usually made of materials that mimic the characteristics of natural animal fur (traditionally real animal skin was used, hence the name 'skin') or of modern synthetic materials that provide similar functionality. Skins have fibres on one side that point backwards and allow the skis to slide forward, but prevent them from sliding backwards, making it easier to climb.