Firestone Pondgard pond liners are made from 45 mil EPDM, which is a synthetic rubber material that is 100% safe for water gardens and fish ponds. The material is durable and will withstand temperatures as low as -40 degress F. Additionally, the material is UV and puncture resistant. The Pondgard pond liner membrane is based on EPDM synthetic rubber, a highly flexible stable waterproofing membrane. PondGard pond liners are specially formulated to be safe for exposure to fish and plant life in decorative ponds. They can easily be shaped to fit the unique contours of any pond. PondGard pond liners show outstanding resistance to the harmful effects of ultraviolet radiation (UV), ozone and other environmental conditions. The pond liners require little or no regular maintenance once installed. 20 year warranty from manufacturer. Pond liner measures 20 X 40. This item cannot be expedited.