What is the Best Pond Liner to Use?

A pond liner has one job: stop water seeping out of the pond into the ground. The right one also keeps the water clean, survives sunlight and handling, and lasts long enough that you never have to drain the pond to replace it.

There are several pond liner materials on the market, and each suits a different kind of pond. Below are the four common types, what they are made of, and where each one works or falls short.

The Different Types of Pond Liners

Flexible pond liners are grouped by the polymer they are made from. Each material trades off cost, stiffness, ease of seaming and how well it tolerates sunlight.

HDPE or the High-Density Polyethylene Pond Liners

HDPE liners are among the most economical liner materials per square metre, which is why they are the usual choice for large ponds, farm ponds, reservoirs and lakes. HDPE is a stiff thermoplastic, not a rubber. It is supplied in thicknesses such as 500, 1000 and 1500 micron (0.5, 1.0 and 1.5 mm), and panels are joined on site by heat (wedge or extrusion) welding.

Advantages: HDPE is strong and durable, costs less than most alternatives, and resists UV exposure and a wide range of chemicals, so it can be left exposed on pond slopes. Welded seams are as watertight as the sheet itself.

Disadvantages: It is stiff and hard to fold into tight curves or small, irregular shapes, so it is a poor choice for a DIY garden pond. Welding needs trained crews and equipment.

PVC Pond Liners

PVC liners are also inexpensive and very common, especially for small ornamental ponds.

Advantages: PVC is light, easy to handle and flexible, so it follows the shape of a small pond without much effort. It resists many chemicals.

Disadvantages: Flexible PVC gets its softness from plasticisers. In sunlight it loses them, turns brittle and cracks, so exposed areas need covering with soil, stone or a protective layer. Some PVC grades can leach additives that harm fish, so check that the liner is rated fish-safe before using it in a fish pond.

RPE or Reinforced Polyethylene Pond Liners

RPE is a polyethylene sheet with a woven reinforcing scrim laminated inside it. It is a common choice for medium-sized ponds and canals.

Advantages: It is pliable and light for its strength, and resists UV, chemicals and punctures. Panels can be prefabricated in large sizes and seamed easily.

Disadvantages: It costs more than plain HDPE or PVC, and the stiffer grades take more care to fit into small, irregular ponds.

EPDM or Ethylene Propylene Diene Monomer Pond Liners

EPDM is a synthetic rubber, widely used in construction for roofing membranes.

Advantages: It is very flexible and strong, easy to shape around ledges and curves, tolerates heat, cold and weather well, and is safe for fish.

Disadvantages: It is expensive compared with HDPE or PVC, and heavy. Joining panels needs special seam tape or adhesive and careful handling, so it is rarely used for large ponds.

HDPE and RPE are both polyethylene, so they are easy to confuse. Our side-by-side RPE vs HDPE pond liner comparison sets out how each is made, where each one fails and how to pick for your pond.

What is the best pond liner material to be used then?

No single material wins on every count. Choose by the pond you are building:

• Large farm ponds, reservoirs and lakes: HDPE, because it is cheapest per square metre, UV-resistant and can be welded into one continuous sheet.
• Small garden or ornamental ponds you are building yourself: EPDM or a fish-safe PVC, because they fold into tight shapes.
• Medium ponds where low weight and puncture resistance matter: RPE.

Then weigh longevity. Once the liner is covered and the pond is filled, you do not want to drain it for repairs, so pick a thickness that suits the subgrade and the depth of water, and lay a geotextile cushion under the liner if the soil is stony.

Ocean Global can help you choose a liner for your pond. See our guide to pond liner cost for typical price factors.