The Beckett 17 ft. x 12 ft. Black PVC Flexible Pond Liner, 20 mil, For Ponds, Water Gardens, Koi Ponds is constructed from weather-resistant 20-mil thick PVC for durability with a 15-year warranty. The liner is suitable for ponds, water gardens, koi ponds, and other fish ponds (not included) and is UV-resistant. This pond liner is the perfect foundation for your pond. A PVC pond liner is more flexible than other liners making it easier to achieve your desired pond shape and size. You can add the Beckett Underlayment underneath the liner to protect the life of your pond liner and your investment. Beckett 7202510 underlayment is designed to cushion the pond liner, providing an extra layer of protection against punctures caused by sharp rocks, gravel, and tree roots. If you have very rocky soil, you may also install a 2 to 3-inch layer of sand first, then the Beckett Underlayment, followed by the PVC pond liner for additional protection. The Beckett 17 ft. x 12 ft. PVC pond liner is ideal for large ponds up to 13 ft. x 8 ft. and 1.5 ft. deep.