Personally I would argue that choosing a pond liner is the most critical decision in your build. Once you have buried it under rocks, water, and fish, you really don’t want to have to replace it – I’ve had to do it before and trust me, it is an awful job.
The best liner for your pond will depend on what budget you have, the complexity of your pond’s overall shape, and also to a lesser extent, whether you have pets or wildlife that might take a dip.
Material Types: Comparison
There are three main materials you will want to consider in the pond liner world. Here is how they stack up:
| Material | Durability | Flexibility | Price | Best For… |
| EPDM (Rubber) | High | Excellent | $$$ | Professional koi ponds and complex shapes. |
| PVC | Medium | Good | $$ | Budget-friendly builds and small garden ponds. |
| RPE (Reinforced Polyethylene) | Extreme | Low | Large lakes or high-puncture risk areas. |
EPDM (Ethylene Propylene Diene Monomer)
This is the gold standard when it comes to pond liner and if you have the budget to do so, the one you should chose. It based on a rubber like material and feels like a thick inner tube.
- Pros: This material is highly UV resistant, and it should realistically last you in the region of 20–30 years. As a bonus it always stays flexible even in freezing temperatures.
- Cons: It can be very heavy depending on the size that you need. It can be punctured by sharp rocks if you don’t get the sand and underlay quite right, or also heron claws if not protected.
- Pro-Tip: Ensure that any material you buy is labeled “Fish Safe.” Some roofing EPDM contains fire retardants or fungicides that are potentially toxic to aquatic life.
PVC (Polyvinyl Chloride)
A lightweight, plastic-based liner.
- Pros: Very affordable and easy to find at hardware stores and garden centres alike.
- Cons: Unfortunately, you will find that it can become brittle over time when exposed to sunlight (UV) and is prone to cracking in colder climates.
How to Calculate the Size
Don’t guess! Use this standard formula to ensure you have enough “overlap” (the extra liner that sits under your edging stones).
Liner Length = Max Length + (2 x Max Depth) + 2 feet (for overlap)
Liner Width = Max Width + (2 x Max Depth) + 2 feet (for overlap)
Example: If your pond is 10 feet long, 6 feet wide, and 3 feet deep:
- Length: 10 + 6 + 2 = 18 feet
- Width: 6 + 6 + 2 = 14 feet
3. The Importance of Underlay
Unless you are very lucky in this regard and find yourself building your dream pond in pure, sifted sand, then fitting underlaym is non-negotiable i’m afraid. It acts as a cushion between the liner and any rocks with sharp edges or roots in the soil.
- Geotextile Fabric: A synthetic material that you will find is readily available in garden centres with an aquatics department as well as online. It is the professional choice and you will find that is a thick, felt-like material designed to sit between the earth and your pond liner of choice.
- The DIY Budget Route: If the budget for your pond is tight and you’ve spent most of it on the best liner you can, then you can use old carpet or layers of wet newspaper. However as a word of caution you will find that these will eventually rot, whereas the geotextile option will last you forever.
4. Key Factors to Consider
- Thickness (Mils): Liners are measured in “mils” (1/1000 of an inch). For EPDM, you want to be aiming for a thickness of 45 mil which is the industry standard for durability. For PVC, you shouldn’t go lower than 20-30 mil.
- UV Resistance: If any part of your liner will be exposed to the sun (e.g., at the water line), it must be UV-stabilized or it will degrade and leak within a few seasons.
- Wildlife: If you have dogs that might jump in or herons visiting, you should go for a thicker RPE or a 45 mil EPDM to prevent claw punctures.
5. Preformed Liners (The “Hard” Option)
These are the rigid plastic tubs you see at garden centers.
- Pros: Impossible to puncture with a shovel; defines the shape for you.
- Cons: As I can tell you from past experience, as good as these look they are very difficult to level perfectly. Also, if the ground settles unevenly unevenly over time, you will sadly find that the plastic can crack under the weight of the water.
