Firestone PondGard Liner is a synthetic rubber material that is made specifically made for ponds and water gardens. No anti-bacterial or anti-fungicide additives are added to this 100% fish safe material. You can be sure your pond liner material will be a safe, healthy aquatic environment for all of your freshwater aquatics. This is a very durable material with cold crack at -40F; that's 40 degrees below zero! UV resistance is excellent for this material.