Pond liners are impermeable plastic membranes used throughout the containment industry for protecting the ground or just for standard containment of water. With that in mind pond liners can be either temporary or permanent. Temporary liners will last (depending on the sub-grade preparation) up to 3-5 years. And long term liners (dependent on sub-grade preparation) up to 20+ years. Studies have been carried out on existing geomembrane liners and some tests have found if properly prepared and cared for, the liner system can last many years past its expectancy.