Closed cell, semi closed cell & Open Cell manufactured by forming a compound of EPDM synthetic rubber. It also called EPT sealers (Ethylene - propylene terpolymer). EPT sealers are joint / space filling materials suitable for use in various applications including automobiles electrical appliance and construction industries. Due to their synthetic rubber construction this product is the world's most durable and weather resistance rubber. The result is that fills virtually any crevice and serves as an effective barrier to heat, water, sound, light and vibration. And with its superior resistance to heat and chemicals, it provides unsurpassed long term stability.