All other rubbers should be measured against natural rubber. For centuries it was the only rubber available, and it was used extensively, even before the discovery of vulcanization in 1839. Synthetic rubbers have been developed either by accident or as the result of pressures of political upheaval or wartime restrictions and consequent unavailability of the natural product. As with other rubbers, many grades and types of NR are available, produced by varying impurity levels, collection methods, and processing techniques. Compounds can be produced over a wider stiffness range with natural rubber than with any other material.
Natural rubber has a large deformability capacity.
This, coupled with its ability to strain crystallize, gives it added strength while deformed. Its high resilience, which is responsible for a very low heat buildup in flexing, makes NR a prime candidate for shock and severe dynamic loads. Thus, in applications where properties such as flexure, cut resistance, abrasion resistance, and general endurance would be adversely affected by heat in less-resilient rubbers, NR is recommended because of its low heat buildup. Natural rubber does have some shortcomings. Degradation from such environments are essentially surface effects that can be tolerated or minimized by using thicker cross sections, by shielding, or by adding antioxidants and antiozonants.