Advantages of Firestone PondGard EPDM rubber pond liner or EPDM rubber geomembrane compared to HDPE or PVC liners: Fish friendly – EPDM rubber liners do not pose any risk to fish, plants or other aquatic life (tested & certified) while PVC is not suitable for Aquatic life as it contains Plasticizers. EPDM can sustain very low temperature as low as minus 45degC, while PVC doesn’t function well at very high and very low temperatures. Hence it is ideal for an indoor pool, or one located in a shady area.