Synthetic rubber or natural rubber. Synthetic rubbers are mainly polymers made from petroleum byproducts. Natural rubber is sourced from the Rubber Tree. Rubber tree's like it hot and humid, therefore: most rubber tree plantations are located in warm tropic and subtropic climates like South America, Southeast Asia and Africa. The Natural Rubber for our flip flops comes from Thailand. The vast majority of rubber plantation in Thailand are owned by family farmers. Rubber tree's are fast growing and the milky white latex (sap) can be tapped once the tree matures to about 6 years old, and with proper care can have a harvesting life of approx 20 years!