What is an HDPE Geomembrane Liner? An HDPE geomembrane liner is a thick, impermeable sheet made of high-density polyethylene. This material is designed to prevent the leakage of liquids or gases, making it perfect for applications that require containment. Whether it's protecting the environment from harmful chemicals or preventing the loss of water in agricultural settings, the HDPE geomembrane liner plays a crucial role in ensuring that projects are completed safely and sustainably.