Sometimes they dry the latex over a fire to form large, black balls called biscuits. Next, they combine various ingredients to plasticize it. Then, they shape the rubber into final products. The last step is to vulcanize the rubber, which gives it strength, hardness and elasticity by treating it with heat and sulfur compounds. The more sulfur compound added, the firmer the vulcanized compound will be.
Manufacturers vulcanize and shape molded products by heating the molds under pressure.
Another type of rubber is called synthetic rubber which is made from chemicals. During World War I, Germany's natural rubber supply was cut off, so they began to make synthetic rubber. The world uses more synthetic rubber than natural as a whole, but the rising cost of petroleum is affecting this. The world could not do without rubber because there is no substitute for it.