In the 19th century, rubber was a rare commodity. Called latex in its raw form, the material came from the sap of “weeping wood” trees found in the Amazon and other parts of Central and South America. Latex could only be harvested about once every two days and, on average, a tree could produce only one cup of sap. The limited availability of rubber facilitated the fad for rubber overshoes imported from Brazil in the 1830s. Considered a luxury item, rubber footwear was about five times more expensive than leather shoes. Despite the high price paid for imported rubber overshoes, pre-vulcanized rubber proved to be an unstable material; it melted in the heat and became brittle in the cold, leading Western inventors to try and find a way to make rubber a more stable and marketable material.