Gordon Low Pond Liner Underlay is recommended to be used underneath all flexible garden pond liners. Gordon Low pond liner underlay is not a simple fleece. The high-quality underlay materials used are superior non-woven mechanically bonded needle-punched polypropylene geotextiles which are sourced from leading European manufacturers. The pond liner underlay offers exceptionally high performance and provide a highly effective protective barrier between substrate and liner. We recommend that you use Gordon Low underlay beneath all our liners as it not only to helps protect liners from penetration by sharp stones roots etc but also to reduce excessive localised stretching of the liner when ground settlement occurs over time. Specifications: 150g/sqm.