Open cell EPDM is the best type of foam rubber sheet for outdoor use. This material is made by adding a foaming agent in the rubber's creation process. The end result is a soft and spongy type of rubber that exhibits superior levels of flexibility and compressibility. Open cell rubber is highly sought after due to its ability to compress under pressure. This is due to the cellular composition of the sheet. The EPDM foam is composed of tiny air bubbles that are spaced further apart from each other. When pressure is applied to the surface of the sheet, the air pockets will get drawn together closely. This results in the sheet compressing down. But once that pressure released, the air pockets will drift apart back to their original place, thus allowing the sheet to rebound back to its normal form. EPDM sponge is best used in outdoor settings. In the world of rubber material EPDM is a rubber compound that is highly resistant to outdoor weathering factors such as UV rays and ozone. Open cell EPDM is better suited to resisting the type of discoloration and cracking that can occur after prolonged UV exposure. This versatile EPDM rubber foam is ideal for industrial sealing and gaskets, as well protective padding from impacts. Open cell EPDM comes in sheets measuring 39" x 78" and is available in thicknesses from 1/8" to 1" to ensure the appropriate amount of protection for any application.