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.