20 mil PVC Pond Liner: For best results protect PVC liner from direct UV Exposure; Adapts readily to a wide variety of fish pond applications; Use in Koi ponds, water gardens & pondless waterfalls;Attaches easily to waterfalls, weirs and skimmers; Flexible and pliable in temperatures -15 to +130;For Koi ponds & pondless waterfalls; Certified fish and wildlife safe; 5 Year Warranty;This Listing Does Not Include UnderGuard Geotextile Underlayment but We Highly Recommend it with all Pond Liners: The biggest contributors to Koi pond, water garden and waterfall failures are poor, unstable soil conditions. Nonwoven geotextile fabrics are 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.;Underlayment is manufactured in 5', 10' 15' widths and will ship to you in one or more pieces equal to the total square footage of the pond liner in liner/geo combo. Simply lay the pieces next to each other and install the pond liner. Use any extra underlayment to create pads for large rocks and boulders placed inside your pond.