Today, most rubber products are made from petroleum, however, natural rubber is preferred in a number of applications, particularly those that involve high pressures and temperatures (such as high performance tires for race cars and airplanes among others). The only natural source of rubber is Hevea braziliensis, a plant grown in tropical regions of the world. Industrial resins are usually derived from wood sources such as pine trees. Efforts to develop alternative sources of these materials suitable for production in the U.S. include Guayule (rubber) and Grindelia (resins).