Made to measure pond liners, box-welded to size
Pond liners made to measure in our UK workshop — rectangular, square, round, L-shaped or bespoke — box-welded from reinforced polymer so the liner sits flat against the basin walls with no bunched corners.
Why a box-welded pond liner beats a folded flat sheet
A flat pond liner is a single rectangular sheet draped into the basin. On an informal, earth-bermed pond that drape is exactly what you want — the membrane follows the contour and the excess fabric tucks into planted margins. In a formal pool, concrete koi pond or rendered block basin, the same drape leaves a bunched fold in every corner that never quite hides.
A box-welded pond liner solves that. The liner is built to the internal length × width × depth of the basin in our workshop: a base panel, four vertical upstands and four hot-air welded corner seams. Once it is dropped into the basin it sits as if it were moulded to it — corners square, walls vertical, no creases visible above the waterline.
We weld in 0.7 mm reinforced polymer (RPM). It is the only mainstream pond membrane that combines factory-weldable thermoplastic seams with a 45-year service life and full fish-safe certification — see the full RPM 0.7 mm spec sheet for the underlying material, or the pond liner comparison for how it sits against EPDM, PVC and butyl.
Rectangular, square, round, L-shaped & bespoke
Every shape below is welded as a single continuous membrane to your dimensioned drawing — no on-site cuts, no taped seams across the corner.
Rectangular pond liners
The most-specified shape for formal garden pools, raised koi ponds and reflecting pools. Box-welded so each corner sits as a sharp 90° fold with no bunching.
Square pond liners
A box-welded square liner is built to the internal length, width and depth of the basin — the four upstands rise vertically against the wall with no excess fabric.
Round pond liners
Round liners are panel-welded from a circular base and a single banded upstand, giving a smooth wall against block, brick or steel ring tanks without darts or pleats.
L-shaped & stepped
L-shapes, returns and stepped sections are welded from the dimensioned drawing as a single membrane — no on-site cuts, no taped seams across the corner.
Bespoke / freeform
Send a measured sketch with key dimensions and we will quote a one-off welded liner. Suits irregular formal features, raised wildlife ponds and architectural water features.
How to measure & order a made-to-measure liner
- 1
Measure the finished basin
Take internal length, width and depth at the deepest point. For round liners measure the internal diameter; for ovals, the major and minor axes. Decide the upstand height — usually the design top-water level plus 50–100 mm of freeboard above it.
- 2
Sketch anything that isn’t a clean rectangle
L-shapes, stepped sections, bays and freeform basins all need a dimensioned sketch — pencil and paper is fine. Mark the internal dimensions of each straight run and the angle of any non-90° corner.
- 3
Cross-check the size
The free pond liner size calculator converts length × width × depth into a flat-sheet size for comparison. The same numbers feed straight into a box-weld quote.
- 4
Send the measurements through
We come back with a welded specification, a current lead time for your size and an installed-cost quote if you would like one of our certified installers to fit it.
Why reinforced polymer is the right membrane for box welding
Not every pond material can be box-welded. Butyl has to be solvent-glued at the seam, which works on a long flat lap but is fiddly and inspection-heavy on a welded box corner. Standard EPDM is tape-jointed for the same reason. PVC is weldable but the seams are weaker than the parent sheet and the material has a short service life.
Reinforced polymer is thermoplastic, so every seam is hot-air welded and tests stronger than the parent membrane. It is plasticiser-free and fish-safe from the day the pond cycles, light enough that even a 4 × 3 × 1 m box-welded liner is a two-person lift, and backed by a 45-year service life.
- Hot-air welded seams test stronger than the parent sheet
- Plasticiser-free and fish-safe from day one
- 0.7 mm membrane at ~0.61 kg/m² — easy to handle on site
- 45-year service life, field-repairable by welded patch
- UV-stabilised top layer — no shade or cover needed
Next steps
Size your basin, compare materials or send your measurements through for a box-weld quote.
Made-to-measure pond liner FAQs
Box welding, supported shapes and how to get a quote.