Depending on the liner type, underlayments are often recommended or even required to protect the liner from damage and leaks. Liner materials that are vulnerable to punctures, tears, and abrasion, such as PVC and EPDM, depend on the protective layer to reduce the risk of damage caused by sharp rocks, roots, or other debris in the ground.
Reinforced pond liners, such as RPE, don't usually require underlayment because their multi-layer construction gives them inherent resistance to punctures, tears, and abrasion. However, in installations where the pond base is not well prepared, an underlayment can help minimize damage.
