Flexibility is key for pond liners to escape damage in extremely low temperatures. As temperatures drop, the liner material can become brittle, which makes it vulnerable to cracking when stressed. Some liner materials remain flexible even in extremely cold temperatures, allowing them to weather the conditions without damage. EPDM remains flexible in temperatures as low as -40°F, for example, while RPE withstands temperatures as low as -58°F, thanks to it's reinforced construction. In contrast, PVC, becomes brittle and vulnerable to cracking at only 0°F. Since EPDM and RPE maintain flexibility even in very cold conditions, they can tolerate disturbances ranging from foot traffic to frost heave without damage.
Even when using a highly cold-resistant liner, it should be well secured with underlayment to prevent damage from ground movement due to frost heave. However, extreme cold can still pose challenges. A tightly stretched liner is vulnerable to excessive ground movement as well as ice expansion, which can tear or damage even a flexible liner if the water doesn't have room to move. For vulnerable liners, consider using floating de-icers to maintain water circulation and prevent freezing at the surface, or draining the water completely until temperatures warm up. A layer of leaves or straw can also help insulate it from temperature extremes.
