Ethylene propylene diene monomer (EPDM) is a type of rubber that is commonly used to make sheets of flexible pond liner. The sheets of EPDM you’ll seen sold as pond liners are thick and heavy, which gives the material durability but makes it hard to install by hand. EPDM is one of the most durable pond liners, but RPE liners are just as strong while being thinner and much more flexible. RPE and RPP liners are also much more likely to be fish safe than EPDM materials. EPDM can be fish safe, but some formulations are designed to cover flat roofing and contains chemicals that aren’t safe at all.
EPDM liner is acceptable enough to leave in place if it’s already installed in a pond and not leaking. However, don’t make it your first choice for a new pond or a relining effort. Thinner and more flexible sheets of RPP and RPE are much more versatile. If you want a gently curving design that shows off every detail of the soil below, you’ll need a thin liner like RPE or RPP. Thick sheets of material like EPDM simply won’t give you the natural look you want from your new water feature.
