There are dozens of flexible liner materials available that allow you to design and build the pond of your dreams, whether that means a chic antique bathtub, a naturalized habitat that supports wildlife of all shapes and sizes, or an elegant koi pond in a formal garden. The best modern liners are durable, flexible, easy to install and repair, budget-friendly, and composed of a dizzying variety of polymers. Since very few of us are materials scientists, it's wise to do some investigating before you settle on one of those pre-cut sheets of mystery plastic you see at the local home improvement store.
EPDM - Ethylene Propylene Diene Monomer Pond Liners
EPDM has been, for years, the go-to material for pond liners of all types. EPDM is a copolymer derived from oil and natural gas and developed to mimic natural rubber characteristics. More frequently recognized now as a roofing material, EPDM is moderately expensive but may still include chemicals that aren't always safe for fish or plants. Liners made from this material are very soft and stretchy, allowing them to conform easily to complex shapes and corners. However, this pliancy means the material is highly vulnerable to punctures and always requires an underlayment. Unlike polyethylenes, EPDM can't be welded with heat but must be taped together in the field. Even heavier than HDPE, EPDM liners for large projects are difficult to ship and install without the help of heavy equipment.
PVC - Polyvinyl Chloride Pond Liners
Do-it-yourselfers often recommend PVC liners specifically for their affordability and ease of installation. Still, they have a host of inherent disadvantages that make the material very difficult to recommend. PVC rests in the middle of the ground between EPDM and RPE in many aspects, like weight and puncture resistance. Other qualities are more concerning: PVC has inferior UV and ozone resistance, which means that liners are likely to rapidly degrade unless buried under at least 12 inches of soil or sediment. This requirement can be burdensome for small pond owners to meet. PVC also doesn't handle temperature extremes, particularly in cold climates where cracks and splits are common.
If that weren't enough, PVC isn't always fish safe. PVC isn't naturally flexible, so manufacturers will add plasticizers like phthalates to compensate. These chemicals are known to leach into pond water. Although information about their effect on fish is not readily available, significant efforts are underway to ban the use of phthalates in products intended for human use. PVC liners can also contain trace amounts of arsenic and other lethal toxins left over from the manufacturing process.
Both EPDM and PVC are older materials still often recommended by pond hobbyists who are more familiar with them. But they both have distinct disadvantages that a newer class of material has largely surpassed them: polyethylene. Our next section dives into detail on the strengths and weaknesses of HDPE, LDPE, and RPE.
