Possibly the oldest known form of natural rubber. Due to its stiffness, it takes the back seat to heva rubber. Unlike heva rubber, one of it's main components is trans-polyisoprene. Most of the polyisoprene in heva rubber has a cis conformation. In its raw form, it is a milky white substance.
Isonandra Gutta trees from the Malay peninsula.
It was introduced to The Royal Society of Arts in London in 1843 by William Mongomerie. That same year, it was used to insulate the telegraph lines along the Great Western Railroad.
S.W. Silver & Co. and company invented a method to extrude it over wire in 1845.
It softens substantially at 71°C and can be formed into many shapes by compression molding or by hand-working at that temperature. It can be cut easily at 60°C.