Trans-1,4-polyisoprene rubber (i.e., PIR, sometimes called Gutta Percha in the past) is a synthetic rubber with properties similar to those of its natural counterpart. It was first industrially prepared during World War II because of a lack of supply of natural rubber but despite containing fewer impurities than natural rubbers and having a simpler preparation process it is not widely used because it is also more expensive. Mechanical properties and chemical resistance is identical to that of natural rubber. As with many other rubbers its mechanical properties can be also improved by the vulcanization process.
