Koi Pond Professional Kit UK | 1.0mm EPDM Heavy Duty Liner + 200gsm Underlay

Koi Pond Professional Kit: 1.0mm EPDM Rubber Liner + 200gsm Underlay

Building a koi pond means digging deep, lining once and living with the result for decades. This kit gives you the two layers that matter most: a 1.0mm heavy duty EPDM rubber pond liner and a matching 200gsm geotextile underlay, cut to the same size and supplied together. 1.0mm EPDM is the specification chosen by professional pond contractors, koi breeders and serious pond keepers across the UK, because it is a third thicker than standard 0.75mm liner. Choose from 17 sizes, from 5m x 4m up to 10m x 10m, to suit ponds of 1.2m depth and more.

Why 1.0mm EPDM works for koi

Thickness where it counts. A koi pond holds many tonnes of water, so every stone or root under the liner is pressed hard against it. The extra material in a 1.0mm sheet spreads that load and resists puncturing better than thinner liners, especially on stony ground or where rockwork and coping sit on the edge.

Rubber that moves with the ground. EPDM is an elastic synthetic rubber. It stretches into corners and over shelves, and it copes with ground settlement and winter freezing without cracking, which stiffer plastic liners can struggle with.

Safe for fish, stable in sunlight. The liner is made with 100% EPDM polymer. It is inert in water, so it does not leach into the pond, and it stands up to UV and weathering, which is why the same material is used to waterproof roofs.

Underlay that is matched, not forgotten. The 200gsm geotextile goes down first and protects the liner from below. Because it arrives in the same size, you are not left measuring and ordering a second product.

Where it is used

The kit suits formal and informal koi ponds, deep goldfish and sturgeon ponds, raised koi ponds built in blockwork or timber with the liner inside, and ponds with filter chambers and bottom drains planned in.

Specifications

Choosing the right size

Measure the longest length, the widest width and the deepest point of the pond. For each direction:

Liner length = pond length + (2 x maximum depth) + 0.6m
Liner width = pond width + (2 x maximum depth) + 0.6m

The 0.6m gives a 30cm overlap on every edge for anchoring under coping. Round up to the next size; sizes work either way round. The table shows the largest pond each kit covers at 1.2m and 1.5m deep, assuming straight sides. Shelves and sloping sides reduce the volume, so treat the litres as an upper limit. A common rule of thumb is about 1,000 litres per adult koi.

Not sure? Use the pond liner size calculator, which also suggests the pump and filter for your pond.

Installation, use and care

Dig the pond, remove every stone and root, and firm the base with 50mm of soft sand. Lay the underlay first, overlapping any joins by at least 300mm, and double it on stony ground or under rockwork. On a warm day, unroll the liner in the sun for 45 to 60 minutes so it relaxes, then lower it in and fold neat pleats at the corners. Fill slowly, easing out creases as the water rises, and only trim the edge once the pond is full. Bed the overlap under the coping.

Koi Pond Professional Kit: Questions Answered

What size Koi Pond Professional Kit do I need for a 4m x 3m pond?

For a 4m x 3m koi pond that is 1.2m deep you need at least 7m x 6m, so choose the 7m x 6m kit. Work it out as pond length (or width) + (2 x maximum depth) + 0.6m, then round up to the next size. Sizes work either way round.

Is the underlay included, and what is it?

Yes. Every kit includes 200gsm needle-punched geotextile underlay in the same size as the liner. On the 5.5m sizes the underlay sheet is half a metre larger, so trim the spare off on site.

Why choose 1.0mm EPDM instead of 0.75mm for a koi pond?

Koi ponds are deep, heavy and often surrounded by rockwork, so the liner works harder. The 1.0mm sheet is a third thicker than 0.75mm, which gives more resistance to stones, roots and foot traffic during the build. It is heavier to handle, so plan for two or three people on larger sizes.

How deep should a koi pond be?

A depth of at least 1.2m is widely recommended for koi, with 1.5m giving more stable winter temperatures and more room for growing fish. Use the size table above to check which kit covers your planned footprint at your chosen depth.

Can the EPDM liner be repaired or extended later?

Yes. EPDM can be patched with EPDM repair sheet and cold-bond adhesive tape, in the same way as butyl. Keep your offcuts after installation, as they make ideal repair patches.

Ordering and delivery

Choose your size above and add to basket. The liner and underlay are cut to size for each order, so they cannot be returned once cut; check your measurements against the size table before ordering. Free UK delivery applies to every size. For sizes not listed, or help with a koi pond design, contact our team.

✅ Trust & Guarantee

• ✅ Fish Safe Certified — Koi and goldfish safe, inert EPDM material
• ✅ Free UK Delivery — All mainland UK sizes delivered free
• ✅ Lifetime Guarantee — Professional-grade lifetime liner warranty
• ✅ Expert Advice Available — Pond contractor and koi specialists on hand

Helpful Guides

• Koi and wildlife pond liners
• Pond liner sizing: measure and order the right size
• Pond liner installation: all guides
• Pond liner materials compared
• EPDM 1.0mm pond liner on its own
• Pond liner underlay
• EPDM pond liners