20' x 20' 20 mil PVC Pond Liner & Underlayment Combo PVC vinyl pond liners are the most cost effective versatile and adaptable liners available. Ideal for ponds of all sizes with steep or gentle sloping sides, tight corners, contours and shelving. Completely safe for fish, plants and wildlife. Attaches easily to waterfall boxes, weirs and skimmers. Remains flexible and pliable even in extreme hot or cold temperatures. UnderGuard Geotextile Underlayment is perfect for stabilizing soil, preventing rocks and roots from penetrating pond liner and for creating rock pads to cushion large rocks and boulders placed in the pond on top of the liner. Standard 5-year warranty for defects in manufacture, materials or workmanship.