A good quality underlay  minimises the possibility of a liner puncture and is also invaluable when used as protection pad when placing larger rocks on to liner. On shale or stoney soils it is a must.

This underlay is a thick woven non perishable textile and provides  protecting to the horizontal sides of your pond walls and terraces unlike sand or newspaper which slips and breaks down over time. The fabric will also helps to reduce  the build up of water or gases under your pond liner by wicking it away.