Great article, worth reading
Spanish explorers encountering an advanced civilization in Mesoamerica in the 16th century had plenty of things to be astonished about, but one type of object in particular was unlike anything they had ever seen before: rubber balls. No such stretchy, bouncy material existed in the Old World, and they had to struggle to find words to describe it.
New research from MIT indicates that not only did these pre-Columbian peoples know how to process the sap of the local rubber trees along with juice from a vine to make rubber, but they had perfected a system of chemical processing that could fine-tune the properties of the rubber depending on its intended use. For the soles of their sandals, they made a strong, wear-resistant version. For the rubber balls used in the games that were a central part of their religious ceremonies, they processed it for maximum bounciness. And for rubber bands and adhesives used for ornamental wear and for attaching blades to shafts, they produced rubber optimized for resilience and strength.
All of these, according to the research by Professor Dorothy Hosler and Technical Instructor Michael Tarkanian of MIT’s Department of Materials Science and Engineering, were most likely achieved by varying the proportions of the two basic ingredients, latex from rubber trees and juice from morning-glory vines, which were cooked together...