45 Mil EPDM Firestone PondGard is a synthetic rubber material that is 100% safe for water gardens and fish ponds. No fire retardant or anti-fungicides are addedto the liner which makes it fish safe. Your pond liner material will be a safe, healthyaquatic environment for all your freshwater aquatics. The material is durable and will withstand temperatures at -40F. This material is UV and Puncture resistant.