Yoga mats are specially fabricated mats used to prevent hands and feet slipping during asana practice in modern yoga as exercise. An early variety made of rubber carpet underlay, pioneered by the yoga teacher Angela Farmer in 1982, was called a sticky mat. Before modern times, meditative yoga and hatha yoga were practised on bare ground, sometimes with a deer or tiger skin rug. Modern mats suitable for energetic forms of yoga are made of plastic, rubber, and sometimes other materials including hessian and cork, trading off cost, comfort, grip, and weight. The yoga mat has been called "One of the most ubiquitous symbols of yoga's commercialization".