EPDM is an elastomeric polymer synthesized from ethylene, propylene and a small amount of diene monomer, compounded with carbon black, processing oils and various cross-linking and stabilizing agents. As a thermoset membrane that recaptures its shape after stretching, EPDM maintains its physical properties for decades. EPDM is manufactured in large sheets varying in width from 10 feet to 50 feet, and features lengths up to 200 feet. The membrane can be reinforces and comes in thicknesses of 45, 60, 75 and 90 mils (thousandths of an inch).