Also known as polyisoprene, natural rubber is vulcanized from the latex of the Hevea brasiliensis tree. Natural rubber was the sole O-ring polymer before the development of synthetic elastomers in the 1930s. Though its use has since sharply declined, natural rubber offers many excellent characteristics, including low heat build up, high resilience and elongation, good abrasion resistance and excellent low temperature flexibility.
Natural rubber has both high tensile strength and good tear strength due to its tendency to strain crystallize. It also undergoes low compression set. Its chief drawback is its poor resistance to oils and solvents. The double bond in its main polymer chain also makes natural rubber susceptible to attack by oxygen, ozone and UV light.