Pond Liners are available in either PVC or EPDM. PVC pond liners are made from durable 30 mil fish grade PVC. PVC pond liners contain UV stabilizers that help protect the liner from breaking down from sunlight. EPDM pond liners are 45 mil thick. You can rest assured that your aquatic life will be safe, because these pond liners contain none of the algaecides & fire retardants found in roofing EPDM. In fact, durable EPDM pond liners are specially formulated for water gardens.