Collection: Pond Liner Underlay UK | 60gsm & 200gsm Geotextile Fleece

Pond liner underlay is the layer that goes between the excavated ground and your liner. It stops grit, stones and roots rubbing against the membrane as the pond fills, settles and moves through the seasons. We sell it in two weights, each in 93 sizes from 2m x 2m up to 45m x 40m, so you can order the same size as your liner and cover the whole excavation.

Which underlay weight do I need?

• 200gsm heavy-duty underlay: the choice for most ponds. Use it on stony, flinty or root-filled ground, under koi ponds, and wherever rocks, plant baskets or heavy edging sit on the liner.
• 60gsm lightweight underlay: a lower-cost separating layer for ground that is already smooth and stone-free, such as sandy soil, sanded beds or boarded raised ponds.

What size underlay should I order?

Order underlay in the same size as your pond liner: pond length plus twice the maximum depth plus the edge overlap, and the same for the width. Our pond planner works out the liner and underlay sizes for you. If your exact size is not listed, choose the next size up that covers both length and width. Where pieces are joined, overlap them by at least 300mm.

New to underlay? Read our pond underlay guides, or browse all pond liners.