Several materials are used in the production of modern balloons.  Natural latex rubber and metalized nylon (sometimes mistakenly called "Mylar") are the most common materials.  Latex is a natural product derived from trees and is biodegradable.  The production of latex is a natural process of many plants, and tapping of the trees does not harm the tree.  Latex harvesting discourages deforestation because latex producing trees are left intact.  A tree can produce latex for up to 40 years.