What is a box welded pond liner?

The definition

A box welded pond liner is an EPDM or Butyl rubber pond liner that has been cut and hot-air welded at the corners and edges to produce a three-dimensional shape — a box — that exactly matches the interior of your pond. Unlike a flat sheet liner, there is no excess material to fold away. The liner simply drops in.

Why the shape matters

With a flat sheet liner, the surplus material at the corners must go somewhere. It gets folded, pleated or tucked — and over time those folds trap sediment, harbour algae and create stress points in the liner material. A box welded liner eliminates this entirely. Every surface lies flat. The base is clean. The walls are taut.

For koi ponds in particular, crease-free corners are not just aesthetic — they prevent the pockets of dead water where harmful bacteria establish. For garden ponds and water features, the improvement is equally visible: the liner disappears and the water takes centre stage.

How it's made

We cut the pond liner material to a precise pattern and weld each corner and edge using hot-air welding equipment. The weld joint is as strong as the parent material — it does not delaminate or fail at the seam. Before any material is cut, we produce a scale drawing of your liner and send it to you for approval. Nothing is manufactured until you have confirmed the dimensions are correct.

What shapes can be box welded?

Any pond with defined geometry can have a box-welded liner: square, rectangular, circular, L-shaped, stepped, or bespoke. The geometry is captured in the technical drawing — that drawing is what we manufacture to. For irregular shapes, we work from a sketch or dimensions you provide and produce the drawing from there.

Box welded vs flat sheet

Flat sheet liners are a sensible choice for informal, freeform ponds where the shape is organic and difficult to measure precisely. For any pond with defined, consistent walls and a flat base, a box-welded liner will always produce a better result. A more detailed comparison is available in our box welded vs flat sheet guide.

Materials and grades

Box-welded pond liners are available in EPDM and Butyl rubber, both in 0.75mm standard grade and 1.0mm heavy duty. The 0.75mm grade suits the majority of garden ponds and water features. The 1.0mm grade is recommended for koi ponds and larger installations where additional robustness is valued. Both carry a 25-year guarantee. If you are unsure which is right for your project, see our material selection guide.

The ordering process

Getting a box-welded liner is straightforward. You provide your pond dimensions, we produce a technical drawing for your approval, and manufacture begins only once you have confirmed the drawing is correct. Standard lead time is 5 to 10 working days from drawing approval. Delivery is included to mainland UK addresses.